Diving Lingo 101: Glossary of Terms, Phrases and Slang


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Diving Lingo

Diving is a rich sport when it comes to names, expressions, and technical words. It is pretty easy to get confused if you are new to the diving scene. I remember going on one of my first boat dives and being asked if I was carrying a sausage. “Huh… I didn’t bring food”, I replied, which caused fits of laughter among my fellow divers. Yes friends, the learning curve was steep. To make it a bit easier for you, we have put together this glossary of the most commonly used diving-related terms, phrases, slang and acronyms.


Alternative air source - is a secondary supply of air or other breathing gas used by the diver in an emergency. Examples include an auxiliary demand valve, a pony bottle and bailout bottle.

Alternobaric vertigo - is the feeling of dizziness, that is caused by the unequal increase in middle ear pressures. Such a state may occur due to barotrauma of descent, and/or the effects of nasal decongestants. When the pressures in both ears reach ambient levels, the the dizziness usually stops. Although most often mild, the vertigo can persist until the diver reaches the surface continuing the unequal pressures, which can damage the inner ear or eardrum.

Altitude diving - diving at a location where the water surface is at an altitude which requires the modification of decompression schedules (more than about 300 m (980 ft) above sea level).

Ambient light - is the available sunlight underwater used as a source of illumination.

Ambient pressure - is the surrounding pressure; on land, comes from the weight of the atmosphere, at depth, comes from the weight of the water plus the weight of the atmosphere.

Analog Instrument - a device that uses a needle moving around a dial to provide information. Compasses, gauges, watches, etc. can be analog instruments. An alternative to analog instrument is digital display.

Anoxia - a medical condition caused by a severe lack of oxygen in the body.

Apnea - is generally defined as a suspension of breathing, however, in the modern athletic world apnea has become a synonym of freediving - a form of underwater diving that relies on divers' ability to hold their breath until resurfacing

Ascent - part of the dive profile where the diver is moving upwards towards the surface. An ascent may be interrupted by stops (decompression stops), when the diver maintains a functionally constant depth for the purpose of decompression.

Ascent rate - is the rate at which depth is reduced at the end of a dive. It is recommended to never exceed the ascent rate of 30 feet / 9 meters per minute, as it is an important part of preventing the decompression sickness.

Atmospheric diving suit - is basically submarine of an anthropomorphic form, with elaborate pressure joints to allow articulation while maintaining an internal pressure of one atmosphere. The ADS allows the diver to go as deep as 2,300 feet (700 m), and eliminates the majority of physiological dangers associated with deep diving. The diver doesn’t need to decompress, nor breathe the special gas mixtures. What’s more, the diver do not even need to be a skilled swimmer. Nowadays, ADS are still very heavy and expensive, thus, are used mostly by rescue teams and military.


Backplate - A plate, usually made from metal, which rests against the diver’s back, and to which the primary scuba cylinders are attached. Held to the body by harness straps over the shoulders and around the waist. It is most often used with a back inflation buoyancy compensator.

Backward roll entry - means of entering the water in scuba gear from a sitting position from the side of the boat. Using this method, the diver needs to securely hold his mask, lean backward and roll into the water with his tank and shoulders first. Checking for an all clear is recommended.

Bailout bottle (also called bailout cylinder) - is a cylinder with an emergency supply of air or other breathing gas, aimed to use in case of air supply trouble.

Balanced regulator - a regulator designed to help the diver maintain a consistent breathing effort regardless of external conditions, such as depth or tank pressure.

Barotrauma - an injury caused by unequal pressures between a space inside the body and the ambient pressure, or between two spaces within the body.

BC - see buoyancy compensator, same as BCD - buoyancy control device.

Bell harness - a safety harness made of strong webbing. The harness is fastened around the diver’s body over the exposure suit, and allows the diver to be lifted without risk of falling out of the harness.

Blind traverse - is a situation when the diver passes through a cave from one entrance to a different exit, which the diver has not used before.

Blue hole - is a large marine cavern or sinkhole, which is open to the surface and may provide access to submerged cave passages. Well-known examples can be found in Belize, the Bahamas, Guam, Australia (in the Great Barrier Reef), and Egypt (in the Red Sea).

Bottom time - the time between descending below the surface to the beginning of ascent. excluding ascent itself and decompression time. Bottom time is used to calculate decompression obligation.

Breath-hold diving - diving without life support apparatus, while holding one's breath, also see freediving and apnea.

Buddy - diving partner. When diving with a buddy, you need to monitor each other constantly during a dive and provide assistance or rescue when needed. Buddy system is created with the purpose to increase divers’ safety.

Buddy breathing - sharing of the same air supply by two or more divers in case of an emergency, in particular when one diver's air supply is exhausted or unavailable due to equipment malfunction.

Buddy line - a short line between two divers, helping them to maintain contact during a dive, most often used in poor visibility, or other conditions where the divers might become separated and not be able to quickly locate each other.

Buoyancy - the upward force exerted on an object in fluid that opposes the weight of an immersed object. Objects that float are positively buoyant, those that sink are negatively buoyant and those that stay where placed are neutrally buoyant.

Buoyancy compensator - an inflatable vest worn by the diver that can be automatically or orally inflated to help control buoyancy; abbreviated BC or BCD.

Buoyancy control - the skill of maintaining the appropriate buoyancy at any time during the dive.


Carbon dioxide - CO2; an odorless, tasteless gas that is a byproduct of metabolism and is excreted by the lungs in exhaled air.

Carbon dioxide toxicity - occurrence of toxic effects, such as headache, shortness of breath or even sudden blackout, caused by the buildup of CO2 in the blood.

Cave diving - a type of scuba diving that involves diving into various overhead environments including caves, abandoned mines or quarries and natural springs or sinkholes where the exit is not always visible. Because such an environment prevents the diver from making a direct vertical ascent to the surface, cave diving requires specialized training and equipment.

C-card (certification card) - a plastic card issued to a diver by a certification agency as evidence of completed diver training and experience required for the level of certification. You may be required to show your certification card when booking a dive trip, hiring scuba equipment or filling dive tanks.

Cf - cubic foot. A measure of volume, often used to mark the size of scuba cylinders. Standard cylinder sizes are 30, 50, 72 and 80 cf.

Closed circuit scuba (also called rebreather diving) - underwater diving, using a rebreather - an apparatus designed to allow divers to re-breath exhaled air after removal of CO2 and addition of supplemental 02. Unlike open circuit systems, closed circuit scuba is noiseless and produces no bubbles.

Command signal - a signal from one diver in a team that requires a response from another diver. Command signals include: Are you OK, Hold, and Surface.

Compressed air - air at a pressure greater than ambient.

Confined water - a dive site, where the water that is enclosed and bounded sufficiently. Confined water is essentially a controlled environment, not affected by geographic or weather conditions, most often used for safe training purposes. The simplest example of confined water is a swimming pool.

Controlled buoyant lift - a rescue technique used by scuba divers to raise an incapacitated diver to the surface from depth

Cyanosis - a bluish coloration on the skin or mucous membranes that appears when the tissues near the skin surface are low on oxygen


DAN - Divers Alert Network, a group of nonprofit organizations that provides emergency and informational advice and assistance for its members and the diving community. Member services usually include a diving accident hot-line, and diving accident and travel insurance. Services to the general public include diving medical advice and training in first aid for diving accidents. DAN America and DAN Europe also collect and maintain databases on diving accidents, treatment and fatalities, used for research and statistical reference.

Deco mix (also called decompression gas) - gas mixture used during decompression in order to to accelerate it. Deco mix usually has increased oxygen content.

Decompression - change from one ambient pressure to a lower ambient pressure that occurs during the ascent. During the decompression, gas pressure within the body is reduced and and dissolved inert gases are eliminated from the tissues.

Decompression algorithm - a set of step-by step procedures, designed to calculate the decompression stops needed for a particular dive profile. The algorithm can be used to generate specific decompression schedules, create decompression tables, or be implemented in dive computer software.

Decompression chamber (hyperbaric chamber) - is a large cylindrical tube, in which the air pressure can be varied to help deep-sea divers to adjust gradually to normal air pressure.

Decompression illness - DCI; a term that encompasses such decompression related problems as decompression sickness and arterial gas embolism.

Decompression sickness - DCS; a general term for all problems resulting from nitrogen leaving the body when ambient pressure is reduced. Can be divided into Type I (musculoskeletal and/or skin manifestations only) and the more serious Type II (neurologic, cardiac, and/or pulmonary manifestations).

Decompression stop - a decompression stop is a pause during the diver’s ascent, made to allow the body to expel dissolved gases, primarily nitrogen, in the blood. Failure to perform decompression stops, leads to decompression sickness, caused by the gases expanding and turning into bubbles. A diver who only breathes gas at atmospheric pressure when free-diving or snorkelling will not usually need to decompress. Divers using an atmospheric diving suit do not need to decompress either, as they are never exposed to high ambient pressure.

Deep diving - a dive deeper than 18 meters (60 feet). This type of diving requires additional preparation, planning and skills.

Deep water blackout - loss of consciousness caused by cerebral hypoxia on ascending from a deep breath-hold dive, when the swimmer does not necessarily experience an urgent need to breathe.

Depth gauge - a device that is calibrated to display how far a diver is below the surface.

Dive computer - a device that allows to monitor the time and depth of a dive as well as calculate nitrogen levels in the body and determine a safe ascent profile using mathematical algorithms. With the help of dive computers divers can extend bottom time beyond what a dive table allows, avoid decompression sickness, etc. Many dive computers also offer additional information such as water temperature, dive log, the pressure of remaining breathing gas, etc.

Dive flag - a flag used to signal that divers are below. There exist two standard versions of a dive flag - a red rectangle with a white diagonal stripe or a blue and white double tailed pennant.

Divemaster - a professional level recreational diver, who has enough skills and expertise to lead a group of less experienced divers underwater.

Dive profile - most often a graph, displaying two crucial characteristics of the dive: depth and time. The profile can be used to determine a dive's likely decompression obligation.

Dive tables (also called decompression tables) - printed cards or booklets that allow divers to determine a decompression schedule for a particular dive profile and breathing gas.

Diving signals - hand and light sign system used by scuba divers to communicate with each other when underwater.

Drift diving - a type of scuba diving, where a diver is transported underwater by drifting with currents.

Drop weight - weight used during descent and ascent, but left on the bottom at the guideline during the deep part of the dive when it is not needed due to suit compression.

Dry bag - a watertight bag or case that allows to keep the desired equipment or documents dry in a wet environment.

Dry suit - A watertight suit, designed to keep the diver dry and provide insulation with a layer of gas, such as air. Dry suits are usually used for diving in cold waters, where the protection of a wetsuit is not sufficient.


EAN - Enriched Air Nitrox. A special breathing gas that contains more oxygen and less nitrogen than plain air. It is used by recreational divers to increase the bottom time or safety margin by decreasing the amount of nitrogen absorbed. The usage of such mixture requires the adherence to strict depth restrictions and some predive testing.

ECCR - electronic closed circuit rebreather. The device uses electronic circuitry to monitor the status of the loop gas in real time, and performs the necessary adjustments to keep it within narrow tolerances.

Eddy - a circular movement of water, formed on a side of the main current. It often appears at a point where the mainstream passes a projection or meets the opposite current.

Electro-galvanic fuel cell - an electrical device designed to measure the concentration of oxygen in dive gear.

Equalization - the procedure used to balance the pressure of a gas filled space with the ambient pressure by forcing air into that space. It diving it is used to offset increasing water pressure and prevent barotrauma or pressure damage.

Exposure protection - a piece of special clothing or a costume that is worn during the dive with the purpose to prevent abrasions and decreases in core body temperature. Exposure protection suits range from thin wetsuits to heavy dry suits.


Faceplate - a glass or a plastic window on a full face mask or a helmet.

Farmer John/Jane - a two-piece wetsuit, where the bottoms cover the torso and the legs all the way to the ankles and the tops cover the torso and the arms to the wrists.

First stage - a diving regulator component that attaches to the tank valve and reduces the gas pressure from that in the cylinder to release it into the hose that supplies the second stage and BC inflation.

Fogging - condensation of water vapour on the inside surface of a mask that results in reduced visibility.

Forward roll entry - a technique of entering the water by a scuba diver from a boat or a pier by bending at the knees and, while firmly securing the mask, rolling forward into the water, landing on one's shoulders and tank.

Free air - air at atmospheric pressure.

Freediving - breath-hold diving, where no scuba equipment is used, also called apnea.

Free flow - malfunction of a demand regulator where the valve sticks in the open position, causing a constant rate of flow.

Frenzel maneuver - one of the methods for equalizing the middle ear by pinching the nose closed and moving the back of the tongue upwards.

Frogman - a scuba diver, specifically a military diver on an undercover mission.

Full-face mask - a diving or snorkeling mask that covers the eyes, nose and mouth and provides the diver with the breathing gas.


Gas blending - mixing breathing gases for diving and filling the diving cylinders with such mixes as nitrox or trimix.

Gas embolism - a condition when a gas bubble enters the blood vessel and blocks it.

Gas fraction - the fraction of a particular gas in a gas mix, by molecular count, volume or pressure.

Gaseous impurities - contaminants in the compressed breathing air or gas mixture.

Gas saturation - a state that occurs when the level of dissolved gas in a particular body tissue has reached its maximum.

Giant stride entry - The most common method used by scuba divers to enter the water. Using this method, a standing diver needs to take a large step into the water while securely holding his mask, tucking chin and bringing fins quickly together to keep himself at the surface for a controlled descent.

Glowstick - a small tube with either a single-use chemical substance that produces light or a battery powered LED bulb.

GPS - a global positioning system that provides location using the ring of stationary satellites. Even very small GPS devices can be used to accurately determine speed and direction of travel, and identify dive site locations. 


Half time (tissue half time) - the 50% of time it takes for a dissolved gas in a tissue (such as nitrogen) to equilibrate to a new pressure, or to reach full saturation at a new pressure.

Hang tank - an extra tank staged at the decompression stop. Typically found at the rear of a dive boat in case of emergencies.

Heliox - mixture of helium and oxygen, usually used as a breathing gas during very deep dives.

Helicopter turn - maneuver in which a diver rotates on the spot on a vertical axis with the help of small fin movements.

Helium - in inert and second lightest gas, used as a component of breathing gas mixtures for deep diving. The benefit of using helium is that it doesn’t cause problems of narcosis to the same extent as nitrogen.

High pressure nervous syndrome (HPNS) - is a disorder that results from using a breathing gas that contains helium, when deep diving. Symptoms of HPNS include tremors, myoclonic jerking, somnolence, electroencephalogram changes, visual disturbance, nausea, dizziness, and decreased mental performance. The severity of the symptoms depends on the mix of breathing gases, and can often be decreased with continued exposure.

Hood - a garment used for thermal head protection. Hoods are usually made from neoprene or latex (for use with dry suits).

Hydrostatic pressure - pressure at a certain point at depth due to the weight of the water above.

Hydreliox - breathing gas containing hydrogen, helium and oxygen used for deep diving.

Hyperthermia - a body temperature higher than normal. In diving hyperthermia can result from overheating in a wet suit.

Hyperventilation - either a rapid and shallow breathing associated with panic, or, in context of freediving, deliberate overbreathing that leads to reduced levels of carbon dioxide in blood and may result in tingling in fingers and dizziness.

Hypothermia - a condition when the body temperature is lower than normal.

Hypoventilation - breathing at an abnormally low rate that leads to elevated carbon dioxide level in blood.

Hypoxia - abnormally low level of oxygen in the body, insufficient to support normal activities or consciousness.


ICD (Isobaric counterdiffusion) - the diffusion of gases in and out of tissues, caused by a change in the composition of the breathing gas under the constant ambient pressure.

Immersion hypothermia - the decrease of body temperature that occurs when the diver is fully immersed in cold water without proper thermal protection.

Inflator valve - a manually operated valve that puts compressed air into the buoyancy bladders of a BCD or into a dry suit.

Ingassing - an uptake of inert (not metabolically active) gases in body tissues during the dive.

Internal condition of cylinder - the state of the internal space of a cylinder regarding corrosion, wear, pitting or rust. Both steel and aluminum cylinders can be corroded internally, if salt water enters the cylinder.

IP (Intermediate Pressure, or Interstage Pressure) - the reduced pressure between the first and second stages of a diving regulator. Also referred to as LP (Low Pressure) in this context.


J-cylinder - bulk gas storage cylinder with internal volume of 50 litres.

Jellyfish - marine animals that are usually transparent and bell shaped. The tentacles, hanging down from their bodies have a stinging mechanism that these creatures use for prey catching and defence. If you get stung by a jellyfish, apply vinegar to the injured skin area.

Jocking strap - a webbing strap system that is used with diving helmets in order to prevent the helmet assembly from being lifted by buoyancy.

Jonline - a short line line with a hook device, often used by scuba divers to fasten themselves to any thickness anchor or down line. Jonline helps the diver to stay in the water column regardless of wave action during decompression stops.

J-valve - a spring-loaded scuba cylinder valve that shuts off a diver’s air supply once the cylinder pressure reaches approximately 300psi. A diver can then open the reserve by pulling a rod, attached to the reserve lever.


Kayak diving - a type of recreational diving, where a diver uses a special purpose kayak to get to the site where the distance from a suitable entry and exit point is inconvenient for shore diving.

Kelp surface dive - a vertical method of descending, when the diver enters the water feet-first. The technique is most often used when diving to unknown depth or when obstructions or heavy plant (such as kelp) growth exists. Some also find it easier to equalize ears using this type of descent, because there is less blood pressure in head than with pike (head first) dive.

Knot - the velocity unit of 1 nautical mile (6080.20 ft.) per hour; equivalent to 1.689 ft. per second. To convert ft. per sec. into knots, multiply the given number by 0.592.

K-valve - the most common valve, used on scuba cylinders. This type of valve has no reserve mechanism and fits regulators with yoke attachments.


Lanyard - a piece of rope or a cord usually worn around one's neck or wrist and used to secure or lower things, such as a knife, compass, etc.

Laryngospasm - an uncontrolled muscular contraction of the vocal cords that causes a partial blocking of breathing in. Laryngospasm is also a body’s response to prevent water from entering the lungs when drowning.

LED - light emitting diode, commonly used in dive lights.Lifeline - a line connected firmly to the diver at one end and anchored at the other end at the diving control point. The lifeline is used as a means to communicate with the diver and assist him/her to the surface and back to the control point, if necessary.

Lift bag - an air-tight bag with straps that can be tied to an object, which, once the bag is inflated, will be lifted to the surface by the means of bag’s buoyancy.

Lift capacity - the amount of buoyancy provided by a BCD. Lift capacity can vary depending on the size of the buoyancy compensator and its intended use, for example, a BC for cold fresh water will provide greater lift capacity than that for warm salt water.

Logbook - a record of the diver’s dive history that serves as a proof of experience. Keeping a logbook is optional for recreational divers, but mostly mandatory for professional divers.

Long hose - 5 ft (1.5 m) to 7 ft (2.1 m) long interstage hose on a scuba regulator, primarily used by cave and technical divers to to simplify air sharing, in particular through narrow spaces.

Lost buddy drill - a standard procedure followed in case dive buddies get separated. Procedures may differ depending on the circumstances and training organisations.

Low volume (low profile) mask - a mask with a little amount of air space inside it. Low volume masks sit closer to the diver’s face and require less air to purge if flooded.


Manifold - a piece of gear used to connect two diving cylinders containing breathing gas, providing a greater amount of gas for longer or deeper dives.

Macro photography - a photography method that allows to get close-up pictures of small subjects and producing an image larger than life size by using Macro accessories attached to the camera's lens.

Mask - a skirted glass window (or multiple lenses) constructed to provide air space between the diver’s eyes and water. It is thanks to the mask that both eyes can see in the same plane underwater. There are many different types of masks, the regular mask covers eyes and nose only; full face masks also cover the mouth. Modern mask skirts are mostly made of hypoallergenic silicone.

Mask squeeze - is a painful condition that appears during rapid descents, when the ambient pressure suddenly increases and the diver neglects to equalize his/her mask. As a result the mask creates suction on the face and eyes that can possibly lead to tissues swelling or even cause permanent damage if the mask is not equalized.

Mixed gas - breathing gas for diving other than air, usually implies a helium based mixture.

MOD/ODL - maximum operating depth/oxygen depth limit. The depth limit a diver can safely achieve using a particular gas mixture. For example, the MOD for EAN32 (32% oxygen) is 40 m.

Monofin - a type of swimfin that consists of a single surface attached to footpockets for both of the diver's feet and is typically used in finswimming or free-diving.

Multilevel diving - a type of dive profile when a diver spends time at several different depths on a single dive.


Narcosis - depressed mental state, a stupor that can range in intensity from confusion or drowsiness to coma.

NAUI (National Association of Underwater Instructors) - a non-profit association of scuba diver training, one of the oldest certifying agencies.

NDL (No decompression limit) - the maximum time a diver can spend at a specified depth without the need to make mandatory decompression stops during the ascent.

Neoprene - a synthetic rubber material that exhibits good chemical stability, maintains flexibility and is used for manufacturing of most wetsuits and some drysuits.

Net cutter - a handle with a hooked blade used to cut netting or fishing line in case the diver gets entangled and needs to free himself/herself or his/her buddy.

Night diving - underwater diving that takes place during the hours of darkness.

Nitrogen - an inert gas that makes up approximately 78% of air. Nitrogen does not enter into any chemical reaction in the body, but can cause problems like nitrogen narcosis and decompression sickness when breathed under pressure.

Nitrogen narcosis - also known as narcs or raptures of the deep, is a reversible alteration in consciousness caused by the diver breathing gases containing Nitrogen at high pressure. Nitrogen narcosis usually does begins to manifest itself at depths of 30 m and greater.

Nitrox - any mixture of nitrogen and oxygen that contains less than the 78% of Nitrogen.No-mount diving - a strategy for diving in a very tight overhead environment, which involves the diver wearing a basic harness or simply hand-carrying cylinders.


Octopus breathing - sharing air using an octopus regulator.

Octopus regulator- a spare demand valve fitted to a first stage diving regulator and used as an alternative air source in case of emergency.

Off-gassing - diffusion of gas out of the tissues into the blood, and its further movement to the lungs where the gas is eliminated by exhalation.

Open circuit scuba - a breathing apparatus that discharges the exhaled air into the environment, with no part of it being re-breathed by the diver.

OOA (out of air) - an emergency situation where the breathing gas supply to the diver has stopped.

Open-water diving - recreational diving done in an environment other than a swimming pool but with no overhead obstacles; for instance, lakes, ponds, rivers, oceans.

OPV (over-pressure valve) - a pressure relief valve that automatically opens at a set pressure to allow excess gas to escape.

O-ring - a loop of elastomer, designed to be placed in a groove and compressed between two or more parts, with an aim to create a seal at the contact surfaces.

Outgassing - diffusion of gas (such as nitrogen) out of the tissue into the blood, and its further transport to the lungs where it diffuses into the lung gas and is eliminated by exhalation.

Overhead - a physical or procedural obstacle to a direct ascent to the surface. An example of a physical overhead would be a cave ceiling, fishing net, ship hull, or wreckage, whereas a procedural overhead is a decompression obligation.

Overweighting - Carrying more weight than is necessary to achieve neutral buoyancy at all times in a dive.

Oxygen - Often seen as using the chemistry abbreviation 02, gas vital for all life on this planet; makes up about 21% of the air by volume.

Oxygen therapy - a treatment that involves breathing pure oxygen or a gas that contains more than 21% oxygen.

Oxygen toxicity - damage or injury caused by breathing oxygen at either too high pressure or concentration.


PADI - Professional Association of Diving Instructors. It is one of the largest certifying agencies.

Panic - a strong sudden sensation of fear which often replaces reason and logical thinking with overwhelming feelings of anxiety and frantic agitation.

Partial Pressure - pressure exerted by a single component (gas) within a gas mixture.

Patent Foramen Ovale - a hole between the left and right atria (upper chambers) of the heart that enables blood flow between them.

Personal Locator Beacon (PLB) - a personal safety device that is designed to indicate a person in distress and help emergency services quickly find him/her.

Pony bottle - is a small diving cylinder, fitted with an independent regulator, and serves the purpose of an alternative air source in case of emergency, such as depletion of the diver's main air supply. The capacity and contents of the pony bottle should be sufficient to allow a safe ascent from any point in the planned dive profile, however its size is usually pretty small, which explains the name pony.

Pre-fill External Inspection - examination of the external condition of a pressure vessel (tank) to ensure that it complies with requirements before accepting for filing.

Pressure - any force exerted over an area.

Pressure Gradient - partial pressure change rate of a dissolved gas through a solvent, which is the driving mechanism for diffusion through the solvent.

Primary Light - the main light to be used on a dive. Usually the most powerful.

Professional Diving - diving which is done as a part of the diver's employment or professional occupation.

Public Safety Diving - the underwater work conducted by law enforcement, fire department rescue, and search and recovery dive teams.

Purge - usually to press the purge button on a demand valve to induce a gas flow to clear the demand valve interior of water or other substances.

Purge Valve - allow masks or snorkels to be cleared easily and without removal.


Quad - a group of high pressure gas storage cylinders mounted upright on a frame and manifolded together. Usually in four, six, nine, twelve, or sixteen cylinder arrangements.

Quick Link - oval connector shaped like a chain link with a screw gate on one side.


Rapture of the Deep - nitrogen narcosis.

Rash Vest (rash guard, rashie) - a shirt made of spandex and nylon or polyester, designed to protect against rashes caused by abrasion, often worn under a wetsuit.

Rebreather - a closed-circuit system which filters exhaled air and recirculates it for rebreathing by the diver. Using a rebreather requires special training.

Recompression - subjecting a diver to pressure after an ascent from a dive as treatment for decompression illness or to prevent decompression sickness. Preferably done in a recompression chamber, but occasionally done as in-water recompression.

Recreational Dive Planner - a decompression table developed by DSAT for calculating no-stop time underwater.

Recreational Scuba Diving - diving for the purpose of leisure and enjoyment, observing the prescribed limits, such as a depth no greater than 30-40 meters, using only compressed air, and never requiring a decompression stop.

Reel - mechanism used to store, deploy and recover long line.

Regulator - in scuba diving, a device that reduces the pressure of a breathing gas and delivers it from the scuba tank to the diver.

Regulator Freeze - malfunction of the regulator mechanism caused by water freezing inside it and locking the mechanism open (free flow).

Repetitive Dive - a dive performed before off-gassing from the previous dive is complete (normally, at least 10 minutes, but no more that 12 hours after a previous dive).

Reserve Gas - gas which is not intended to be used during the dive, and is reserved for contingencies.

Residual Gas - gas remaining in a cylinder from the previous fill.

Residual Nitrogen Time - the time it would take to off-gas any extra nitrogen remaining after a dive. Residual Nitrogen Time is always taken into consideration when determining the safe duration for any repetitive dive.

Reverse Profile - either a repetitive dive, deeper than the previous dive, or a multilevel dive in which a later level is deeper than an earlier level.

Reverse Squeeze - pain or discomfort in enclosed spaces, such as sinuses, middle ear, inside mask, due to inability to release pressure on ascent from a dive.

Rip Current - a strong current flowing outward from the shore. Such currents can be dangerous to the uninitiated swimmers, but are often used by divers to facilitate entry to areas beyond the bar or reef.


Safety Sausage - an SMB or a surface marker buoy. A buoy towed by a diver to indicate location to people at the surface.

Safety Stop - a voluntary stop (not required by the decompression schedule) on ascent from a dive. The diver spends a specified time at a specified depth (normally, 3 minutes at 5 meters / 15 feet), for purposes of nitrogen off gassing.

Samba - contractions experienced by breathhold divers when approaching hypoxic blackout.

SASY/SASA - Supplied Air Snorkeling for Youth/Supplied Air Snorkeling for Adults. BC-like Personal Flotation Device, mounted with small compressed air cylinder and regulator that allows snorkeler to breathe comfortably on the surface, but prohibits him/her from descending.

Saturation - the degree to which a gas is dissolved in the blood or tissues, full saturation occurs when the pressure of gas dissolved in the blood or tissues is the same as the surrounding pressure of that gas.

Scuba (SCUBA) - acronym meaning Self Contained Underwater Breathing Apparatus.

Scuba Orienteering - competitive underwater sport in which scuba divers attempt to swim a circuit marked by buoys, without surfacing, using compass navigation and mechanical distance measurement. Points are awarded for time and accuracy according to the specific course definition and length.

Second Stage - a part of the diving regulator which provides pressure reduction from intermediate pressure to ambient pressure on demand.

Shallow Water Blackout - a sudden unconsciousness, caused by hypoxia, that occurs among some breath hold dives. Often occurs near the surface after a deeper dive.

Shore (Beach) Diving - scuba diving that starts from the shore line.

Sidemount - a scuba diving equipment configuration which has diving cylinders mounted alongside the diver, below the shoulders and along the hips, instead of on the diver’s back.

Skandalopetra - a flat stone, usually of marble or granite, weighing between 8 and 14 kg (17-30 lbs), with rounded corners and edges and tied to a rope. Historically skandalopetra was used by Greek free-divers to assist descent. When the diver wanted to ascend, he would signal the tender on the boat who would then pulls in the rope. Currently a competitive sport.

Slate - rigid plastic tablet used for writing messages or notes during the dive.

Snorkel - bended tube with a mouthpiece used for breathing air from above the water surface when the wearer's mouth and nose are submerged.

Snorkeling - swimming at the surface of the water while breathing through a snorkel. The snorkeller is almost always equipped with a diving mask or swim goggles, and fins.

Snorkel Keeper - a device used to hold a snorkel in place at the side of a diving mask by fixing it to the mask strap.

SNUBA - a surface-supplied compressed air apparatus, used for diving in shallow, calm waters. The air is delivered to one or more divers through a long hose.

Solo Diving - the practice of scuba diving alone without a "dive buddy".

Speargun - a weapon for shooting fish underwater. A speargun is usually loaded with a barbed steel spear that can be propelled a short distance forward using stored energy from stretched rubber strips or compressed air behind a captive piston.

Spearo - slang term for breathhold spearfisher.

Standard Operating Procedure - a procedure, usually compiled by a diver certification organisation, prescribing the processes to be followed when performing specified tasks.

Submersible Pressure Gauge - gauge to monitor air supply during the course of a dive.

Surface Consumption Rate - a measure of the diver’s rate of gas usage expressed in psi, bars or cubic feet per minutes. SCR is commonly used in calculations for determining air consumption rate at various depths.

Surface Interval - length of time on the surface between two consecutive dives.

Surface Marker Buoy - a buoy towed by a diver to indicate location to people at the surface.


Task Loading - a multiplicity of responsibilities leading to an increased risk of failure on the part of the diver to undertake some key basic function which would normally be routine for safety.

Technical Diving - a form of diving that exceeds the limits of recreational scuba diving and carries greater technical complexity as well as higher inherent risk. Technical divers often use multiple breathing gases, helium based gases, closed circuit rebreathers, and dive under extensive overheads.

Test Pressure - pressure at which the cylinder is hydrostatically tested for revalidation. Usually 1.5 of working pressure.Thermocline - intersection between two layers of water that are of distinctly different temperatures, usually the colder layer is deeper.

Thumb the Dive - terminate the dive by signalling exit to surface at a time or place other than the planned turning point.

Toynbee Maneuver - a method of equalising the middle ears by pinching the nose and swallowing.

Travel Gas - gas mixture used for descent and/or ascent when the bottom gas is not suitable for breathing at shallower depths.

Traverse - pass through a cave by entering at one point and exiting at another.

Triangular Profile - a dive profile in which, the diver descends at a constant rate, and, after a short bottom time at maximum depth, maintains a constant, slow ascent to the surface or first decompression stop.

Trimix - mixture of helium, nitrogen and oxygen, used for deep diving.

Trim Weight - ballast weight used to improve diver's trim.

Turn the Dive - start the return on a dive which has reached the planned turning point in terms of depth, time, gas supply or distance.


Unbalanced Regulator - a regulator that is affected by tank pressure. The tank pressure works to force the piston in the first stage open. As the gas in the tank diminishes, it is easier for the piston to be forced into a closed position. This makes it increasingly harder to breath from the first stage as the dive progresses. This is an older style regulator and has almost disappeared from today's scuba equipment market.

Underwater Breathing Apparatus - equipment used to supply breathing gas to the diver.

Upstream - against the current or flow.

Upwelling - a vertical water movement that occurs when the surface water is moved away (offshore) due to winds blowing from north to south. Because water from somewhere has to fill the space left by the offshore movement of surface water, water fills in from below, creating a vertical current.


Valsalva Maneuver - a method of middle ear equalization by pinching the nose shut and blowing gently.

Vasoconstriction - the constriction of the blood vessels in order to reduce heat loss from the blood through the skin.

Vasodilation - the widening of blood vessels resulting from relaxation of smooth muscle cells within the vessel walls, particularly in the large veins and arteries.

Vertigo - the feeling of dizziness and off balance that can be a sign of ear barotraumas form minor ear squeeze to perforation of the eardrum.

Visibility - the distance a diver can see underwater measured in feet or meters.

Visual Inspection - internal and external inspection of a pressure vessel as part of revalidation procedure.


Wall Diving - a form of diving on rocks and reefs that run vertically, usually from shallow to deep.

Water Pressure - force per unit area exerted by the weight of water, each 33 feet of seawater exerts a pressure equivalent to one atmosphere.

Weighting System - a set of weights, generally made of lead, to counteract the buoyancy of other diving equipment, and belts, pockets or harnesses used to support them.

Wet Filling - a method of filling scuba cylinders using a water bath to cool them.

Wet Notes - a small notebook made from waterproof paper.

Wet Pot - water filled hyperbaric chamber.

Wet Suit - a garment, usually made of foamed neoprene, that provides thermal protection thanks to the bubbles of gas enclosed within the material. In addition to thermal insulation, wetsuits also provide abrasion resistance and buoyancy.

Whip - flexible high pressure gas hose with the connector at the free end, designed for temporary connections, such as filling cylinders, oxygen transfer, decanting gases when blending gas, etc.

Wing - back inflation buoyancy compensator cell.

Working Pressure - maximum filling pressure rating for the cylinder at standard temperature.

Wreck Diving - diving on natural or man-made shipwrecks.


Yoke Adaptor - a fitting used to connect a regulator or whip with a DIN thread connection to an international connection cylinder valve.

Yoke Valve/Fitting - a fitting or valve used to connect a regulator or filling whip to a diving cylinder using the international connection.

Y-valve - dual orifice valve.


Zip Tie (also cable tie, tie wrap) - self-locking plastic strip used to connect objects together.

Z-knife - line cutting tool with a replaceable blade in a slot.

Have we missed a diving term, name or expression? Leave your questions and/or suggestions of terms to add in the comments below!

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