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Here is a glossary of terms, acronyms, and definitions used in either cave diving or diving in general. If you want to be able to understand more technical details of this sport, reading this glossary would be a good start. Click here (M - Z) to go to the M - Z section.

4 Levels Of Cave Diver Training	Cavern Diver, Intro-To-Cave Diver, Apprentice Cave Diver, and Full-Cave Diver
5 Rules Of Accident Analysis	Be trained, Run a continuous guideline to the entrance, Leave 2/3 of your gas supply for the exit, Use the right gas mix for the right depth, Carry at least 3 lights per diver
50/50 Mix	A gas mix used for decompression at 70 ft after a very deep dive which contains 50% O2 and 50% nitrogen
Accident Analysis	The process of reviewing the causes (& contributary factors) of deaths in underwater caves & incorporating those findings into future dive training
Advanced Cave Dive	Any dive that exceeds the parameters of full-cave training. i.e. stage, scooter, exploration, sidemount, deep, or survey diving. Also indicative of conditions of a cave or tunnel that may be very low, silty, low vis, blown out, multiple navigation decisions, virgin, or subject to collapse.
Air Break	A cave diver is wise to take a 5 minute "air" or backgas break every 20 minutes from 100% O2 during deco. Over time, O2 will burn up the lungs.
Air Embolism	A serious injury where a diver holds his breath as he ascends. The compressed air expands from reduced pressure and ruptures areas of the lungs
Air Pocket	A place on the ceiling of a submerged cave where air (often from a diver's exhaled bubbles) has accumulated to form an air space. You should never breathe this though.
AL	Stands for aluminum which is what many tanks are made of. It's lighter & cheaper than steel. Many rec divers use them. Tech divers use them as stage bottles.
Alternate Exit	Another hole/entrance to the same cave system you are diving, but did not use to enter the system.
Ambient Light	The "glow" from natural light at the cave's entrance. You may not see the entrance light directly, but you can see its glow from around the corner or wherever.
Analyzing The Mix	Processes of using an oxygen analyzer to confirm the % of oxygen in the gas mix. Important for avoiding oxygen toxicity.
Argon	Gas carried in a small tank (pony bottle)used for drysuit inflation for deep dives when diving trimix.
Backgas	Gas carried in the double tanks on the diver's back.
Backmount	A gear configuration where the main gas supply is carried in doubles on the divers back. May also refer to the size of a passage meaning that a diver wearing doubles on his back could fit through the area as easily if he were diving sidemount.
Back-To-Back Arrows	A line marking indicating an equal distance between either two different exit points or an equal distance back to the same exit point if the tunnel creates a circuit.
Backup Lights	Each cave diver carries 2 additional lights on all dives as a back-up should the canister light fail.
Basin	The open water portion of a spring or sinkhole.
BC/BCD	Buoyancy compensator/buoyancy compensator device worn to offset the weight of the diver and gear to make him neutrally buoyant in the water column.
BV/VU/EV	Short for beginning total volume at the dive's start. Volume used during the entire dive. And ending volume left over at the end of the dive. Good for dive planning for future dives and in calculating SAC rates.
Bedding Plane	The low area between two larger masses of earth. One is usually over the other. The height of the space is very limiting, but the width is usually large. The opposite of a joint or virticle rock fissure.
Bends/Getting Bent	Nitrogen bubbles have formed in tissue because they couldn't be removed by the body due to the too short deco.
Blown Out	Condition of the cave where it's undivable due to low vis.
Blue Hole	Cenote in the Bahamas.
Bottle	Another name for a tank
Bottom Mix/Gas	Refers to the gas used at your deepest depth, often times what is in your doubles. Usually when referring to deep dives using trimix.
Bottom Time (BT)	Time elapsed from the beginning of descent to the first deco stop.
Bottom Timer	Instrument worn on the wrist that records max depth, current depth, temp, and bottom time.
Branch/Side Tunnel	A tunnel that connects to the main tunnel. An alternate direction to go.
Bubble Check	Each buddy checks the other for gas leaks around the valves and manifold.
Buddy Awareness	Knowing where your buddy is and his condition at all times. He should be within an arm's reach.
Buddy/Safety/Bail Out Bottle	Extra tank carried by the diver but only breathed in an OOA emergency.
Buoyancy Control	The ability to make oneself neutrally buoyant in the water column, Neither sinking nor ascending.
Butt-Mounted	Referring to where the diver wears his primary (canister) light. It's an old method, but a lot of sidemount divers still use it.
Canister Light	The tube-looking canister worn on the diver's right side or on his butt. It's the primary light.
Carbon Dioxide Build-Up	When the diver is overexerting himself and the body isn't eliminating CO2 quick enough. Can lead to overbreathing the reg or unconsciousness.
Cave Conditions	Referring to the strength of current flow of water, or visibility of the water.
Cave Cookie	Plastic circle with notches similar to the line arrow but is used as a non-directional marker placed on the line. It replaces the clothespin.
Cave Diver	Minimum certified Intro-To-Cave Diver, but mostly referring to Full-Cave certified divers.
Cave Navigation	Using line markers and visual awareness to get back out of the cave.
Cave Zone	The zone beyond the cavern zone where there is no ambient light to be seen, deeper than 70 ft, further than 130 linear feet inside the overhead environment.
Cavern Zone	The entrance area of the cave, but not the cave zone. Within 70 ft of depth, ambient light, and 130 ft of linear penetration.
C-Card	Certification card. Needed for showing proof of training when attending dive sites.
Cenote	A blue hole in Mexico.
Chamber Ride	Recompression treatment for the bends that looks like a metal chamber.
Chimney	Tunnel continuation that goes down like a chimney through a rock slit that is tight from top to bottom but wide from side to side.
Circuit	Entering and exiting from the same entrance point, but part of the exit does not follow the same path as the penetration.
Clean Up	Referring to stowing stage regs, deco bottles, lights, etc when preparing to reach a deco stop or surfacing.
Clothespin	Old tool used to provide non-directional informational markings on the line. It's been replaced by the cave cookie.
COD	Short for contingency operating depth. All diving mixes have a COD which is the absolute max depth you can dive the mix to stay within the 1.6 ATA PPO2 exposure for that mix. Exceeding this depth greatly increases your risk of an O2 hit.
Condom/Catheter	Male drysuit divers use what looks and works like a condom when diving in a drysuit so they can urinate if needed through the P-valve.
Cutting Tables	Using a deco computer program like DecoPlanner or V-Planner to give you a custom dive profile given your dive plan & gas mixes. This is a lot cheaper than buying a dive computer. Can also be used as a backup to a dive computer.
Danglies	Any piece of equipment that falls below the slipline of the diver. It creates drag, damages the cave, reduces streamlining, damages the equipment, looks bad, and creates entanglement hazards. Anything clipped must be tucked too.
Daylight Zone	That are of the cave entrance where you can still see the ambient glow of the entrance light. Also called the cavern zone.
Debris Cone	Occurs when dry land collapses into an underground & underwater tunnel. The cone is in the middle and often seperates the upstream and downstream tunnels.
Deco	Short for decompression and often refers to one's decompression obligation after a dive.
Deco Obligation	The amount of time required for a diver to stay at a certain depth given a certain O2 % to allow nitrogen that's been absorbed into the body tissue to be expelled without forming bubbles which causes the bends.
Deco Planner/V-Planner	Computer programs which can custom cut dive tables for you for a given dive profile and multiple gas mixes. Much cheaper than buying a dive computer. Can be used as a backup to a dive computer.
Deco Schedule	It's the series of stops required by the diver to offgas.
Deco Stop	The depths at which a diver stops to offgas absorbed nitrogen from his system in order to avoid the bends.
Decorations/Formations	The way the water has shaped the cave. i.e. stalactites/stalagmites or the changing landscape of the tunnel.
Deeper Stop	Portions of a deco obligation or schedule where there is a stop that's deeper than the common 20 ft stop.
DIN	Short for a 3-word German name which refers to a connection at the end of a regulator's first stage which screws into the tank valve. It's more secure than a yoke.
DIR	Short for Doing-It-Right which is a totality dive philosophy which focuses on health, strict gear configuration, and standards. No room for individual taste in gear selection in the name of safety.
Distance Marker	Often times a line arrow that was permanently placed on the line which points to the direction of the nearest exit as well as its distance.
Dive Computer	An expensive gadget worn on the diver's arm that uses deco theory and algorithms to calculate the diver's deco stops and obligations. A backup like custom cut dive tables to this is required.
Dive Plan	The planning phase of a dive where safety, protocol, team order, emergency scenarios, objectives, etc are discussed and agreed upon.
Dive Profile	The depth a diver dives in relation to bottom time. Often referred to as a square dive profile if he stays at one depth until beginning to surface.
Dive Slate	A small rectangle of plastic that has a pencil connected to it where the diver can write short notes to his buddy or record dive data.
Double Arrows	Line arrows pointing in opposite directions on a permanent line indicating two alternative exit directions which are equal distance. If they are both pointing in the same direction, then it indicates a jump nearby.
Double Stage	Diving with 2 stage bottles (AL 80's) on the left side of the diver used to extend the diver's range into the cave beyond a single stage dive.
Doubles	Referring to two tanks usually connected together via a manifold with isolator valve. Usually are steel 95 or 104s.
Downstream	Referring to the siphoning side of a sinkhole. The flow is going into the cave rather than out.
Drysuit	A thermal exposure protection suit worn by cave divers to withstand the cooler water temperatures over long durations. Unlike a wetsuit, a drysuit actually keeps the diver completely dry.
DUI	Short for Divers Unlimited International which is a major supplier of drysuits.
EAD	Short for equivalent air depth. Used when diving nitrox to determine your NDL's for that mix given the reduced amount of nitrogen in the mix. It shows the depth that this mix is equivalent to if you were diving its equivalent on air.
END	Short for equivalent narcotic depth. Calculation used when diving trimix that tells the air equivalent of diving the nitrogen portion of a trimix mixture to a particular depth.
Exploration Reel	Reel used by cave explorers in virgin cave to lay line as they explore. Can have between 800 - 1,200 ft of #24 line.
Extended Range	Carrying more gear (i.e. stage bottles) or a different gas mix in backgas to either dive deeper or go further into a cave than only doubles or normal gas mixes would allow.
First Stage	The part of a diver's regulator that connects to the tank valve and reduces the tank's pressure down to an intermediate pressure and delivers it to the second stage which reduces the pressure further to a breathable pressure.
Fragile Cave	A cave that either has formations like stalactites or stalagmites, or a texture of limestone that is brittle to the touch.
Frog Kick	Propulsion technique used by cave divers the most. It looks like the breast stroke in swimming. It's the most forceful while at the same time allowing the cave diver a second in between kicks to glide as he rests.
Gap	End of one line and the beginning of another. You use a jump reel/spool to make the connection.
Gas Matching/Dissimilar Tanks	Calculations made by a dive team where at least one diver is wearing a different size set of doubles than the rest of the team. They ensure that they all use the same cubic feet of gas, not necessarily the same pressure (pounds per square inch).
Gas Switching	Switching regulators underwater at the end of the dive from bottom mix to deco mix. Could also be when switching from a travel mix to bottom mix.
Gas/Gas Mix	What the diver breathes during the dive. It's rarely ever air and is only oxygen at deco. Most usually it's nitrox for regular cave diving and trimix for deep cave diving.
Gator Wraps	Elastic velcro straps worn on the drysuit diver's shins which helps keep air from running into the feet of the suit.
Gave The Thumbs Up/Thumbed The Dive	Another term for "called the dive". Basically, saying the dive is over. We need to surface.
Gear Configuration	They way the cave gear is worn & where. Sometimes even referring to the type of gear worn. Usually has a reason behind every placement.
Gear Modification	The process of taking your gear as bought and modifying it to suit diving in a cave. Part of it is removing danglies and getting things to sit in the right gear configuration.
Gold Line	The main permanent line in the main tunnel of a cave. It's actually gold, a little thicker, and distinguishable from side tunnels' lines.
GUE	Short for Global Underwater Explorers. The most comprehensive cave diving training in the world.
Halocline	A place where fresh water floats on top of saltwater. Kind of like a thermocline in that it may also have a temperature change with it.
Hand/Light Signals	Standard signals dive buddies use to communicate quickly with one another. Some are with their light beams while others are with the hand while being lit by his light.
HID Light	Short for high intensity discharge primary canister light. It's quite expensive, but is the best light available on the market.
Hogarthian Configuration	Mr. Hogarth came up with the configuration of routing the long (7 ft) hose around the diver's neck, breathing it, and donating it in an out-of-gas situation.
HP	Short for high pressure tank which is a tank that is designed to be filled to 3,500 psi, but only gets it's working capacity's volume. As opposed to overfilling low pressure tanks.
Hydro	Short for hydrostatic test. A test done on tanks every 5 years.
Hyperoxic Trimix	A mix of trimix where the oxygen content is higher than 21%.
Hypoxic Trimix	A mix of trimix where the oxygen content is lower than 21%. Quite often around 18% and even below 16% which isn't breathable at the surface.
Independent Doubles	Double tanks worn on the back in backmounr or on the sides in sidemount where they are not connected by a manifold. It's critical to manage gas supplies in each tank when running independents.
Isolator Manifold	A bar that runs between two tanks when diving backmount. It allows the gas from both tanks to be used as one whole and creates redundancy. The isolator is a valve in the middle that can be shut off by the diver. This makes each tank operate as an independent.
IUCRR	Short for International Underwater Cave Rescue & Recovery which is an organization that provides rescue and recovery services when needed.
Jamming The Reel	Occurs when the diver allows line from the reel to loop off the reel's spool and getting lodged in the axle of the reel. Requires fixing before more line from the reel can be used.
Joint	Virticle rock fissure where two large portions of earth meet which are beside one another. It's opposite of a bedding plane. The walls are very narrow, but the height is rather open.
Jump	Going from one permanent line to another. Often times going from the main tunnel to a side tunnel. Using a jump spool/reel is the proper way to set/make the jump.
Jump/Gap Reel/Spool	A reel or spool with about 50 ft of line on it used to connect one line to another whether doing a gap or jump.
Land Owner Relations	Keeping good relations with the land owners of cave diving sites by always asking permission to dive and cleaning up after oneself.
Laying Line/Push	Laying #24 line in a virgin cave while exploring that will be left there permanently for use by other cave divers in the future.
Lead	A virgin cave passage that appears to have potential for going a great distance or connecting to another known passage.
Line Arrow	Plastic triangle used by cave divers to mark the direction of the nearest exit by placing it on the permanent line when a direction decision will need to be made on the way out.
Line Connection/Tie In	What you are doing when you make a jump or when you clip off the primary reel onto the main line at the beginning of the dive.
Line Drill	Drill where the divers OK the line, close their eyes and practice moving towards the cave entrance by following the line as if in a siltout situation.
Line Marker	A line arrow, cave cookie, or clothes pin used by a cave diver on a permanent line to either mark the direction of the exit or a point of interest in the cave.
Line Protocol	The standards that cave divers follow when running guideline in a cave. It's the consideration you give for other dive teams diving the cave at the same time. i.e. not running your line OVER the line of someone else.
Line Trap	A place in a tunnel where the line you laid or the permanent line falls into a restricted area where a diver can't easily follow.
Line Wrap/Placement	A method for laying line which helps prevent laying line into a line trap by looping it around rock projections in larger portions of the cave.
Localized Silting	Condition created when a careless diver silts up a portion of a cave passage. It's localized because you can usually move past it fairly quickly and doesn't destroy vis throughout the entire cave.
Long Hose	The 7ft hose run from the right post, under the canister light, across the chest, behind the neck, and into the mouth. It's the reg that the diver will donate when his buddy is out of gas.
Lost Line Drill	A drill done where the diver takes his safety reel/spool moves of the permanent line and practices finding the line again using his spool with his eyes closed.
LP	Short for low pressure tank which is often referred to as a steel tank rated to 2640 psi with a 10% overfill rating. This is the same tank that is frequently overfilled by cave divers to get more gas.

Click here (M - Z) to go to the M - Z section.