Recreational diving has its own terminology that can be confusing for beginners at first. What does BCD mean? What’s the difference between Open Water and Advanced certification? And what exactly is a no-decompression limit?
In this glossary, you will find explanations of all the basic terms used in recreational diving – from equipment and certifications through safety procedures to basic physiology. Each term is explained clearly and concisely so you can quickly grasp the essence.
Use the navigation above for quick access to the letter you’re looking for.
🤿 Quick alphabetical navigation
A
Advanced Open Water Diver (AOWD)
Advanced diving certification following Open Water Diver. Includes specialized dives (deep, navigation, and three electives).
Alternate air source (Octopus)
A backup second stage regulator, usually yellow in color, used for sharing air with another diver in an emergency situation.
Ascent
The phase of the dive moving toward the surface, should be slow (max 9-10 m/min) with a safety stop.
Atmosphere (ATM)
A unit of pressure. 1 ATM equals pressure at sea level (1 bar). Every 10 m of depth adds 1 ATM.
B
Bar
A unit of pressure used in diving. 1 bar = approximately 1 atmosphere. A standard diving cylinder contains 200-300 bar.
Battery (Dive equipment battery)
Special batteries for dive computers and lights, often lithium or rechargeable, resistant to pressure and water.
BCD (Buoyancy Control Device)
An inflatable vest allowing buoyancy control underwater by adding or releasing air.
Bootie
A neoprene boot protecting the feet, used with open-heel fins or for walking on rocky shores.
Bottom time
Total time spent underwater from descent to the start of ascent. Used for calculating decompression limits.
Buddy diving
Basic safety principle – always diving in pairs, where divers monitor and help each other.
Buoyancy
The buoyant force acting on a diver. We distinguish positive (floats up), negative (sinks), and neutral buoyancy.
Buoyancy control
The ability to control your position in water by adding/releasing air from the BCD.
C
Calibration
Setting and checking the accuracy of diving instruments, especially important for computers and analyzers.
Certification (C-card)
A card confirming completion of a diving course and authorization to dive to a certain depth and under specific conditions.
Cold water
Water with temperature below 15°C, requires special thermal protection (thick wetsuits or dry suit).
Compass
A magnetic or digital compass for underwater navigation.
Console
A set of instruments (pressure gauge, depth gauge, compass) combined in one housing on a hose.
Coral reef
An underwater ecosystem formed by corals, requires gentle approach from divers.
Current
Water movement, can be mild or strong. Requires special techniques and dive planning.
Cylinder (Tank)
A high-pressure container for compressed air, typically steel or aluminum, with a volume of 10-15 liters.
D
DCS (Decompression sickness / “The bends”)
An illness caused by nitrogen bubble formation in the body during rapid ascent or failure to follow decompression limits.
Depth gauge
An instrument measuring dive depth, can be mechanical, digital, or part of a dive computer.
DIN valve
A type of regulator connection to the cylinder using threads, more robust than yoke, used in Europe and technical diving.
Dive briefing
Pre-dive briefing including dive plan, entry/exit location, depth, signals, and safety procedures.
Dive computer
An electronic device monitoring dive parameters and calculating safe limits in real time.
Dive flag
A red flag with white diagonal (international) or red and white striped (USA) signaling the presence of divers.
Dive light
A diving light for night diving, caves, or viewing colors at depth.
Dive log (Log book)
A book or electronic record of all dives with data about location, depth, time, and notes.
Dive medicine
A field of medicine dealing with health aspects of diving.
Dive tables
Tables indicating maximum times at various depths for safe diving without decompression stops.
Divemaster (DM)
The first professional diving level, guide and instructor assistant, can lead certified divers.
Drift diving
A type of dive where divers let themselves be carried by the current, the boat follows them by buoy.
Dry suit
A watertight suit used in cold waters, insulation is provided by an air layer and undergarments.
E
EAN (Enriched Air Nitrox)
See Nitrox.
Emergency ascent
A rapid ascent to the surface in a critical situation.
Entry technique
Method of entering the water – stride (giant stride), backward roll (backroll), from shore, or controlled jump.
F
Fins
Basic diving equipment extending the legs and enabling efficient underwater movement. Can be open-heel or full-foot.
Finning techniques
Various kicking methods – flutter kick (alternating kicks), frog kick, modified flutter.
First stage
The part of the regulator attached to the cylinder, reduces high pressure from the cylinder to intermediate pressure (9-10 bar).
Float
A small float used for marking position or as part of safety equipment.
G
Gauge
An analog indicator of pressure, depth, or other measurements on diving instruments.
Giant stride
Water entry from a high boat deck with one large step forward with hands on equipment.
Gloves
Neoprene gloves protect hands from cold, scrapes, and stings. Banned in some places due to coral protection.
H
High pressure hose
A hose connecting the pressure gauge to the first stage, carries full pressure from the cylinder.
Hood
A neoprene hood protects the head and neck from heat loss. Up to 40% of heat is lost through the head.
Hyperventilation
Excessive breathing before diving, dangerous – reduces the urge to breathe and increases risk of unconsciousness.
Hypothermia
Dangerous body hypothermia, manifests as shivering, slowed reactions, loss of coordination.
I
Inflator
A mechanism on the BCD for adding and releasing air, controlled by buttons or pulling the hose.
Inflator valve
A valve for connecting the hose from the first stage to the BCD or dry suit.
Instructor
A certified professional diver authorized to teach and certify new divers.
J
Jacket
See BCD / Buoyancy Control Device.
L
Lead weight
Weights of various masses for adjusting diver buoyancy.
Log book (Dive log)
A book for recording all dives, confirmed by instructors or divemasters.
Low pressure hose
A hose carrying intermediate pressure (9-10 bar) from the first stage to the second stage, BCD, or dry suit.
Lycra suit
A thin suit for protection from sun and jellyfish in warm waters, without thermal insulation.
M
Mask
Basic equipment creating an air space in front of the eyes, allows seeing underwater.
Master Scuba Diver (MSD)
The highest level of recreational diver (PADI), requires Rescue Diver and 5 specialties plus 50 logged dives.
Maximum depth
The highest recommended depth for a given certification (Open Water 18 m, Advanced 30 m, Deep Diver 40 m).
Mouthpiece
The silicone or rubber part of the second stage that the diver holds in their mouth.
N
NDL (No-Decompression Limit)
The maximum time that can be spent at a given depth without the need for decompression stops.
Neck seal
A seal at the neck on a dry suit, can be neoprene or latex.
Neoprene
Synthetic foam rubber used for wetsuits, gloves, and hoods, provides thermal insulation.
Neutral buoyancy
A state where the diver neither sinks nor rises – a basic skill for efficient and safe diving.
Night diving
A diving specialty after dark, requires lights and special procedures.
Nitrox (EAN – Enriched Air Nitrox)
Air enriched with oxygen (typically 32% or 36% O₂), allows longer dives with lower decompression obligation.
O
Octopus (Alternate air source)
See Alternate air source.
Open Water Diver (OWD)
Basic diving certification allowing independent diving with a buddy to 18 m depth.
O-ring
A rubber seal on valves, regulators, and hoses, requires regular inspection and replacement.
Oxygen analyzer
An instrument for measuring oxygen content in breathing mixture, used when diving with nitrox.
P
PADI (Professional Association of Diving Instructors)
The world’s largest diving organization issuing certifications.
Partial pressure
The pressure of an individual gas component in a mixture, important for calculating oxygen toxicity and narcosis.
Pre-dive check (Buddy check)
Equipment check before the dive – BWRAF (BCD, Weights, Releases, Air, Final OK).
Pressure
Force acting on a surface, in diving increases with depth (every 10 m = +1 bar).
Pressure gauge (SPG – Submersible Pressure Gauge)
An instrument displaying the amount of air in the cylinder in bars or PSI.
Purge button
A button on the second stage or mask for draining/blowing out water.
R
Rebreather
An advanced breathing system recycling exhaled gas. CCR variants for recreational use.
Recreational diving
Diving for fun within the limits of 40 m depth without decompression stops.
Regulator
A device reducing air pressure from the cylinder to breathable pressure, consists of first and second stages.
Rescue Diver
A certification focused on problem prevention and rescue of divers in distress.
S
Safety stop
A recommended 3-5 minute stop at 5 m depth before surfacing, reduces the risk of decompression sickness.
Seal
Sealing elements on a dry suit at the neck, wrists, and ankles.
Second stage
The part of the regulator that the diver holds in their mouth, delivers air on demand during inhalation.
Shorty
A short wetsuit (short sleeves and legs) for warm waters.
Signaling
Underwater communication using hands, light, or other signals.
SMB (Surface Marker Buoy)
An inflatable buoy released during ascent to mark divers’ position.
Snorkel
A tube allowing breathing at the surface without lifting the head from water. Part of basic equipment.
SPG (Submersible Pressure Gauge)
See Pressure gauge.
SSI (Scuba Schools International)
One of the main international diving organizations.
Surface interval
Time spent on the surface between two dives, important for nitrogen off-gassing from the body.
T
Tank (Cylinder)
See Cylinder.
Tank valve
A valve on the cylinder allowing opening and closing of air flow, can be DIN or Yoke.
Thermal protection
Protection against body heat loss – wetsuit, dry suit, or combination of layers.
Training
Structured education under the guidance of a certified instructor.
Trilaminate
Three-layer material used for dry suits, more durable than neoprene but less thermally insulating.
Trim
Horizontal body position in water, optimal for efficient movement and lower air consumption.
U
Underwater navigation
Orientation underwater using compass, natural reference points, and kick counting.
V
Visibility
The distance one can see underwater, affects safety and dive planning.
W
Waterproof seal
A seal preventing water ingress, used on dry suits, watches, and instruments.
Weight
See Lead weight.
Weight belt
A belt with lead weights to compensate for the buoyancy of neoprene and the body.
Weight system
A system for carrying lead weights – belt or integrated into BCD.
Wetsuit
A neoprene suit that allows water in, insulation is provided by a layer of water between the body and the suit.
Wreck diving
A diving specialty on shipwrecks or aircraft, requires special training for penetration.
Y
Yoke valve (A-clamp)
A type of regulator connection to the cylinder using a clamp and screw, common in USA and recreational diving.