Ever wondered what all those diving ancronyms, slang and jargon mean? Well has the answer…


  • A-Clamp:A type of connection between a regulator first stage and the cylinder. It is shaped like an A, hence the name, and fixes with a yolk screw.
  • Altitude Diving  diving at a location where the water surface is more than about 300 m (980 ft) above sea level, and which requires special dive tables or dive computers to calculate allowed depths and times for safety.
  • Ambient pressure  the pressure on the diver at a given depth. 1 atm (100 kPa) at the surface, increasing by approximately 1 atm (100 kPa) for each 10 metres (33 ft) of depth.
  • Anoxia  absence of oxygen caused by inhaling a breathing gas that contains no oxygen or being unable to inhale any breathing gas.
  • Arterial Gas Embolism  a medical condition caused by gas bubbles in the bloodstream that can be caused by a too rapid ascent, in which a gas expands and a bubble blocks the arterial flow of blood.
  • Aqua-lung  underwater breathing equipment consisting of a diving cylinder and diving regulator.
  • AutoDSMB :Same as a DSMB, except the unit is fitted with a small air cylinder that allows inflation without the need to use the divers primary breathing gas source. Specifically used by rebreather divers.


  • Barotrauma  injury caused by pressure
  • Beach master or dive marshal  A person on the beach who records when divers enter and exit the water. Typically used during scuba classes to keep track of the students, watch the gear, provide assistance when required.
  • Bends -A slang name for decompression sickness.
  • Bounce dive  In commercial diving, bounce diving is the alternative to saturation diving. In recreational diving, a bounce dive is a descent to maximum depth and then an ascent back to the surface with the least delay, in a dive profile resembling a spike.
  • Bow -The front of a boat
  • Buddy breathing  Two divers sharing the same demand valve, generally after an out-of-gas emergency
  • Buddy check  a procedure carried out by SCUBA divers using the buddy system where each diver checks that the other’s diving equipment is configured and functioning correctly just before the start of the dive
  • Buddy diving  the use of the buddy system by scuba divers and is a set of safety procedures that improve divers’ chances of avoiding or surviving accidents in or underwater by diving in a group of two or three divers.
  • Buoyancy control  the ability of a diver to control his or her depth – an essential practical diving skill
  • Buoyancy compensator or BCD, or BC  diving equipment worn by divers to provide life-saving emergency buoyancy and the ability to control ascent and descent rates.


  • C-card or Certification card  plastic card issued to a diver by a certification agency as evidence of completed diver training and of experience required for the level of certification.
  • Canoe diving  utilizing a canoe to transport scuba divers and their equipment to offshore diving locations which are beyond practical swimming distances.
  • Carbon monoxide poisoning  the toxic effects of carbon monoxide in the breathing gas, usually due to compressor maintenance errors.
  • Carbon dioxide poisoning  the toxic effects of carbon dioxide, sometimes due to incomplete elimination of carbon dioxide resulting from skip breathing, or excessive work of breathing, or due to scrubber failure in a rebreather system, or inadequate ventilation in a diving chamber or free flow helmet.
  • Controlled buoyant lift  is an underwater diver rescue technique used by scuba divers to safely raise an incapacitated diver to the surface from depth
  • Compressor  a machine used to increase the volume of usable air in a diving cylinder by raising its pressure.
  • Controlled emergency swimming ascent (CESA)  Emergency technique to surface, usually when no breathable gas is available at depth.


  • Decompression illness  DCI is caused by two different mechanisms: decompression sickness (DCS) and Arterial Gas Embolism (AGE), which result in overlapping sets of symptoms.
  • Decompression sickness  a potentially lethal diving disorder caused by bubbles of inert gases, such as nitrogen or helium, coming out of solution and becoming trapped in the tissues, organs and blood vessels of the body causing symptoms ranging from rashes to death. Also commonly referred to as DCS.
  • Decompression stop  a pause during the ascent phase of the dive to allow safe release of inert gases from the tissues of the body and avoid decompression sickness.
  • Decompression chamber: Another name for a hyperbaric chamber
  • Decompression tables  Printed tables that provide divers with a way of avoiding Decompression Sickness by giving the maximum times that can be spent at depth, and by indicating the Decompression Stops and Surface Intervals needed for a particular depth and time profile to be carried out safely.
  • Decompression buoy  a small buoy on a line that divers inflate underwater to indicate their location to their boat. Demand valve  a valve, generally placed in the diver’s mouth, which provides gas from the diving regulator when the diver inhales.
  • DIN:Another type of regulator/cylinder connector. This type is a screw-threaded and favoured by the Europeans and technical divers
  • Dive club  a group of people with an interest in SCUBA diving.
  • Dive flag  Flag used by a boat to indicate that it has ‘divers down’. Comes in two versions: the international maritime signal flag (international code letter flag ‘A’, ) and the red and white flag (red with white diagonal, ).
  • Dive profile  A dive profile is a two dimensional graphical representation of a dive showing depth and time. The profile is often used when describing a dive’s likely decompression obligation.
  • Dive shop  supplier of diving equipment or training, or organizer of dive expeditions.
  • Dive tables  see Decompression tables. Diving regulator  one or more valves in series, which let the gas out of a gas cylinder in a controlled way, lowering its pressure at each stage.
  • Diving signal  a form of sign system used by SCUBA divers to communicate when underwater.
  • Divemaster  A professional level diver who leads a group of less experienced divers underwater. Drift diving  a type of recreational diving where the diver is transported by the currents caused by the tide or in a river. Drowning  death caused by inability to inhale anything but water.
  • DPV-This stands for Diver Propulsion Vehicle. These come in many forms from units that strap to a dive tank to torpedo shaped devices that a diver holds on to
  • Dry suit  a diving suit designed to thermally insulate and provide protection to the skin of the diver.
  • Dysbarism  medical conditions resulting from changes in ambient pressure.


  • Electro-galvanic fuel cell  an electrical device used to measure the concentration of oxygen gas in diving equipment.
  • Equivalent air depth  a way of approximating the decompression requirements of breathing gas mixtures that contain nitrogen and oxygen in different proportions to those in air, known as nitrox.
  • Equivalent narcotic depth  a way of expressing the narcotic effect of a breathing gas mixture, for example trimix.


  • Fraction of gas  (Fg) Indicates the percentage of a gas present in a breathing mixture such as nitrox and trimix.
  • Fill: A slang word for refilling the gas in a dive cylinder.
  • Flood:A term no underwater photographer wants to encounter as it means water is on the wrong side of their housing.
  • Frogman  A scuba diver, particularly a military diver on an undercover mission.
  • Full-face diving mask  a type of diving mask that seals the whole of the diver’s face from the water and contains a mouthpiece or demand valve that provides the diver with breathing gas.


  • Gas blending  filling diving cylinders with gas mixes such as nitrox or trimix.
  • Gas embolism  a potentially lethal diving disorder caused by air or other gas bubbles entering the blood stream through wounds.


  • Half mask  The standard mask style used by recreational scuba divers which provides an air space over the eyes and nose, but not the mouth.
  • Hard Hat diving  Surface supplied diving, generally in professional diving, either wearing a modern diving helmet or the old-style standard diving dress and brass helmet. Helmet diving  see Hard hat diving.
  • Heliox  a gas blend of Helium and Oxygen in which helium replaces the normal Nitrogen in air allowing diving at greater depths than can be done with air.
  • HPNS  High Pressure Nervous Syndrome or Helium Tremors – caused by using breathing gases that contain helium at depth.
  • Hypercapnia  carbon dioxide poisoning generally caused by rebreathing your own exhaled carbon dioxide. A big problem at depth especially with rebreathers or high rates of exertion.
  • Hyperventilation  either a deliberate and dangerous method intended to extend the duration of a free dive or the body’s response to hypercapnia.
  • Hypoxia  insufficient oxygen in the body – normally caused by inhaling a breathing gas that contains insufficient oxygen to support normal activities or consciousness.
  • Hypothermia  a potentially lethal medical condition caused by cooling the body.


  • Interstitial emphysema  gas trapped in the chest after lung barotrauma.
  • J-Valve  An early yoke style scuba tank valve that had a lever which activated a reserve pressure release and was commonly used before the submersible pressure gauge was available.


  • K-Valve  A standard yoke style valve without a reserve lever.
  • Kayak diving  an alternative to boat diving or shore diving where the diver uses a special purpose kayak to get to site.
  • Log Book  List of the dives a diver has recorded for proof of experience.


  • Mask on forehead  (MOF) placement of mask on the forehead when not in actual use before, after or in between dives.
  • Maximum operating depth  (MOD) the depth at which the partial pressure of oxygen (ppO2) of a gas mix exceeds a safe limit.


  • Navy SEAL  A US Navy trained military diver.
  • Night diving  a dive at night – many underwater animals are nocturnal or behave differently at night.
  • Nitrogen narcosis  condition caused by breathing nitrogen at high pressure (at depth). (aka “rapture of the deep”)
  • Nitrox  a breathing gas consisting of oxygen and nitrogen


  • O-ring: Found all over scuba equipment. O-rings are made of rubber and keep water out.
  • Oxygen toxicity  is caused by using breathing gases that contain oxygen at high pressure (at depth).
  • Partial pressure of a gas  a measure of the concentration of individual component gases of breathing gases.
  • Pneumothorax  collapsed lung.
  • Pony-A small back-up cylinder used as an emergency air source in case their primary fails
  • Professional diving  diving for payment.


  • Rebreather  breathing equipment that captures, cleanses and re-oxygenates exhaled breath so that it can be re-inhaled.
  • Recompression chamber  a pressure vessel used to treat divers suffering from certain diving disorders such as decompression sickness.
  • Recreational diving  a type of diving that uses SCUBA equipment for the purpose of leisure and enjoyment.
  • Reef hook:A large hook connected to a strong rope which connects to a diver’s BCD. This allows him/her to remain stationary in a current while not damaging any coral or fingers.
  • Regulator  see Diving Regulator


  • Salt water aspiration syndrome  the diver inhales a mist of sea water from a faulty demand valve causing a reaction in the lungs.
  • Saturation diving  a decompression regime used in commercial diving that allows divers to live work for weeks at a time where their tissues become saturated in high pressure gas.
  • SCUBA -Self Contained Underwater Breathing Apparatus. Basically it’s your commonal garden regulator and dive cylinder. Add the two together and you have a scuba unit.
  • Secondary drowning  can occur hours after a near drowning.
  • Semi-dry suit  a wet suit with wrist and ankle seals to reduce entry and exit of water.
  • Shore diving  Scuba diving that starts from the shore line.
  • Skin  a lycra suit worn by a diver in warm water or under a wet suit.
  • Snorkeling (or snorkelling)  the practice of swimming at the surface of a body of water while equipped with a diving mask, a shaped tube called a snorkel, and usually swimfins.
  • Solo diving  the practice of scuba diving alone without a “dive buddy”. Standard diving dress  old-fashioned “hard hat” diving gear.
  • Subcutaneous emphysema  gas under the skin tissue.
  • Submersible pressure gauge or SPG  Gauge attached to the regulator and used to monitor pressure remaining in the scuba cylinder Surface detection aids  equipment, such as flags, SMBs, flares, EPIRBs and whistles, carried by divers to maintain contact with dive boats or attract rescue when lost at sea.
  • Surface interval  the time between dives. Divers need to track this time interval for planning decompression for the next dive.
  • Surface marker buoy, SMB  a small inflated buoy that divers tow when underwater on drift dives to indicate their location to their boat.


  • Technical diving  a form of SCUBA diving that exceeds the scope of recreational diving allowing deeper and longer dives.
  • Time to fly  Divers must wait approx. 24 hours after the last dive before flying to reduce the risk of decompression sickness.
  • Trimix  a breathing gas consisting of oxygen, helium and nitrogen.


  • Wall diving  diving along the face of a vertical wall – requires good buoyancy control because there is no seabed to prevent the diver descending too deep.
  • Weighting system  weights, generally made of lead, to counteract the buoyancy of other diving equipment, such as diving suits and aluminium diving cylinders.
  • Wet suit  A tightly fitting neoprene thermally-insulating diving suit that allows a limited volume of water inside the suit.
  • Wreck diving  diving on shipwrecks.

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