Scuba Diving Glossary: 60 Diving Terms Every Beginner Should Know

Every hobby has its own language, and scuba has more than most: acronyms, gear names, physics terms and boat slang. You don't need to memorise all of this before your course, but knowing the basics will make briefings and theory lessons much easier.

Equipment terms

Scuba

Self-Contained Underwater Breathing Apparatus. Diving with your own air supply.

Tank / cylinder

The metal bottle that holds compressed breathing gas, usually aluminium or steel. See scuba tanks.

Regulator ("reg")

The device that reduces high tank pressure to breathable pressure. It has a first stage on the tank and a second stage in your mouth. See regulators.

Octopus ("octo")

A spare second stage, usually with a yellow hose, for sharing air with a buddy in an emergency.

BCD / BC

Buoyancy Control (or Compensator) Device. An inflatable jacket or wing that lets you adjust buoyancy. See BCD guide.

Inflator / power inflator

The button unit on the BCD hose that adds or releases air.

SPG

Submersible Pressure Gauge. Shows how much air is left in your tank, in bar or psi.

Console

A housing that groups the SPG, depth gauge and compass.

Dive computer

A wrist device that tracks depth and time and calculates your no-decompression limit. See dive computers.

Air-integrated (AI)

A computer that reads tank pressure wirelessly or by hose.

DIN / Yoke (INT)

The two ways a regulator connects to a tank valve. Yoke clamps over it; DIN screws in.

Weight belt / integrated weights

Lead weights worn on a belt or in BCD pockets to help you sink.

Wetsuit / semi-dry / drysuit

Exposure suits that keep you warm. See wetsuit guide.

SMB / DSMB

(Delayed) Surface Marker Buoy. An inflatable tube sent to the surface to show boats where you are.

Open-heel / full-foot fins

Fins worn with boots (open heel) or on bare feet (full foot). See fins.

Physics and physiology

Bar / ATA

Units of pressure. At sea level you are at 1 bar; every 10 m of seawater adds about 1 bar.

Equalizing

Adding air to your ears (and mask) to match rising water pressure as you descend. See equalization.

Squeeze (barotrauma)

Pain or injury caused by pressure differences in air spaces such as ears, sinuses or mask.

Nitrogen narcosis

A drunk-like effect of breathing nitrogen under pressure, usually noticeable from about 30 m. It goes away as you ascend.

Decompression sickness (DCS, "the bends")

Illness caused by dissolved nitrogen forming bubbles in the body after ascending too fast or staying too long/deep.

Lung overexpansion injury / AGE

Serious injury caused by holding your breath while ascending. Arterial Gas Embolism is the most severe form.

No-decompression limit (NDL)

The maximum time you can stay at a given depth and still ascend directly (with a safety stop) without mandatory decompression stops.

Decompression stop

A required pause during ascent to let nitrogen leave the body safely. Recreational divers stay within NDLs so they never need one.

Safety stop

A recommended 3-minute stop at about 5 m at the end of every dive. See ascent and safety stop.

Surface interval (SI)

Time spent on the surface between dives, allowing nitrogen to off-gas.

Residual nitrogen

Nitrogen still in your body from a previous dive, which shortens the next dive's NDL.

Air consumption / SAC rate

How quickly you use air. SAC (Surface Air Consumption) is measured in litres per minute.

Buoyancy and skills

Neutral buoyancy

Neither sinking nor floating; hovering weightlessly. It's the most important skill in diving. See buoyancy.

Positive / negative buoyancy

Tending to float up / sink down.

Trim

Your body position in the water. Ideal trim is horizontal, like a swimmer.

Weighting

Carrying the right amount of lead. Overweighting is a common beginner mistake.

Fin kick (flutter, frog kick)

Different finning techniques. The frog kick is gentle and stirs up less sand.

Mask clearing

Pushing water out of your mask by exhaling through your nose.

Regulator recovery

Finding and replacing your regulator if it leaves your mouth.

CESA

Controlled Emergency Swimming Ascent. An emergency ascent while exhaling, taught in Open Water courses.

Giant stride / back roll

Two common ways to enter the water from a boat.

People, planning and paperwork

Buddy

Your dive partner. You look after each other throughout the dive. See buddy system.

Buddy check (BWRAF)

The pre-dive equipment check: BCD, Weights, Releases, Air, Final OK. See buddy check.

Divemaster (DM)

A professional dive guide who leads dives and assists instructors.

Instructor

A professional certified to teach and certify divers.

C-card

Your certification card, now usually digital.

Logbook

A record of your dives (paper or app). It proves experience and helps you track progress.

Dive briefing

The talk before each dive covering the site, plan, depth, time and safety procedures.

Fun dive

A guided dive for certified divers, not part of a course.

Refresher / ReActivate / Scuba Review

A short course to brush up skills after a long break from diving.

Gases and types of diving

Nitrox / EANx

Enriched Air Nitrox. Air with more oxygen (commonly 32% or 36%), giving longer no-decompression limits within shallower maximum depths.

MOD

Maximum Operating Depth. The deepest you can safely go on a given gas mix.

Trimix

A gas mix with helium used in deep technical diving.

Drift dive

A dive where you let the current carry you along the reef. See types of dives.

Wall dive

A dive along a vertical reef wall.

Shore dive / boat dive

Entering from the beach or from a boat.

Liveaboard

A boat you live on for several days of diving. See liveaboards.

Muck diving

Diving on sand or silt to find small, unusual creatures.

Visibility ("vis")

How far you can see underwater, in metres.

Thermocline

A sudden change in water temperature at a certain depth.

Frequently asked questions

What is the octopus in scuba diving?

The octopus is a spare second-stage regulator, usually yellow, that you or your buddy can breathe from if one of you runs out of air.

What does NDL mean?

No-Decompression Limit: the longest time you can stay at a certain depth and still return directly to the surface (with a safety stop) without mandatory decompression stops. Your dive computer shows it continuously.

What is neutral buoyancy?

It is the state where you neither sink nor float, so you hover effortlessly in the water. You achieve it with correct weighting, small BCD adjustments and controlled breathing.