Diving glossary

145 terms explained in plain language.

Safety, medicine, decompression

• Ascent rate (9–18 m/min)
• Barotrauma — pressure-related injury
• Buddy system (always dive with one)
• Bühlmann ZH-L16 algorithm
• CO₂ buildup (skip-breathing risk)
• DAN — Divers Alert Network
• DCS — Decompression Sickness
• Decompression stop (mandatory)
• Deep stop (mid-depth pause)
• Flying after diving (DAN guidelines)
• Gradient factors (GF Low / GF High)
• Hyperbaric chamber (recompression)
• Hyperventilation (and freediving danger)
• IWR — In-Water Recompression
• Lost buddy procedure (1-minute search rule)
• NDL — No-Decompression Limit
• Nitrogen narcosis (rapture of the deep)
• Out-of-air procedures and air sharing
• Oxygen first aid for diving accidents
• Oxygen toxicity (CNS, pulmonary)
• Oxygen window — inspired/expired pressure delta
• PFO — Patent Foramen Ovale
• RGBM — Reduced Gradient Bubble Model
• RSTC Medical Statement (dive medical form)
• Safety stop (5 m / 3 minutes)
• Samba — Loss of Motor Control (freediving)
• Saturation diving (commercial)
• SWB — Shallow Water Blackout

Gear & equipment

• Air-integrated computer (tank pressure transmitter)
• Aluminum 80 (AL80) tank
• BCD — Buoyancy Compensator Device
• Underwater compass
• DIN tank valve (European standard)
• Dive computer (depth, time, NDL)
• Dive mask (single, twin, frameless)
• Dive torch / underwater light
• Drysuit (cold-water exposure suit)
• First stage regulator (tank → HP/LP)
• Neoprene hood (thermal protection)
• Integrated weights (in BCD pockets)
• Octopus (alternate air source)
• Paddle fins (stiff blade)
• Primary donate (long-hose configuration)
• Rebreather (CCR — Closed Circuit)
• Reel and spool (line management)
• Regulator (1st + 2nd stage)
• Second stage (mouthpiece + demand valve)
• Sidemount (twin tanks side-mounted)
• SMB — Surface Marker Buoy
• Snorkel (surface breathing tube)
• SPG — Submersible Pressure Gauge
• Split fins (efficiency design)
• Stage bottle (deco / bailout gas)
• Steel HP/LP tanks
• Trim weights (back / shoulder)
• Twinset / doubles (tech)
• Weight belt (lead in pouches or block)
• Wetsuit (neoprene exposure suit)
• Wing BCD (rear inflate)
• Yoke (A-clamp) tank valve

Training & certifications

• Advanced Open Water Diver
• Cavern and Cave Diver progression
• CMAS — Confédération Mondiale des Activités Subaquatiques
• Cross-agency certification recognition
• Deep Diver specialty (to 40m)
• Divemaster (first professional level)
• Drift Diver specialty
• EFR — Emergency First Response (CPR/AED)
• GUE — Global Underwater Explorers
• IANTD — International Association of Nitrox and Technical Divers
• NAUI — National Association of Underwater Instructors
• Night Diver specialty
• Enriched Air (Nitrox) Diver specialty
• Open Water Diver certification (entry)
• Open Water Scuba Instructor (OWSI)
• PADI — Professional Association of Diving Instructors
• Rescue Diver certification
• SDI/TDI — Scuba Diving International / Technical
• Search & Recovery specialty
• SSI — Scuba Schools International
• TDI Intro to Tech (tech foundation)
• Trimix Diver (helium-based gas mixes)
• Underwater Navigator specialty
• Wreck Diver specialty

Physics, gas laws, pressure

• Air compressibility under pressure
• Boyle's Law (pressure × volume)
• Dalton's Law (partial pressures)
• EAD — Equivalent Air Depth
• END — Equivalent Narcotic Depth
• FN₂ — Fraction of Nitrogen
• FO₂ — Fraction of Oxygen (Nitrox notation)
• Halocline (salinity layer)
• Henry's Law (gas dissolution)
• MOD — Maximum Operating Depth
• How NDL is calculated (compartments)
• Negative buoyancy
• Neutral buoyancy (and trim)
• Positive buoyancy
• PpN₂ — Partial Pressure of Nitrogen
• PpO₂ — Partial Pressure of Oxygen
• Pycnocline (density layer)
• RMV — Respiratory Minute Volume
• SAC — Surface Air Consumption
• Salt water vs fresh water buoyancy
• Thermocline (temperature layer)

Marine biology

• Barracuda species
• Coral bleaching (mass mortality)
• Cuttlefish (Sepiidae)
• Fire coral (sting hazard)
• Frogfish (Antennariidae)
• Hammerhead shark species
• Lionfish (venomous, invasive Caribbean)
• Manta ray — Mobula alfredi / birostris
• Mola mola — Ocean sunfish
• Nudibranch (sea slug)
• Octopus species seen diving
• Reef shark species (blacktip, whitetip)
• Scorpionfish (camouflaged venomous)
• Sea turtles — green, hawksbill, loggerhead
• Seahorse species (pygmy, common)
• Stonefish (most venomous fish)
• Thresher shark — Alopias
• Whale shark — Rhincodon typus

Site features & geology

• Atoll (ring-shaped reef)
• Barrier reef (separated by lagoon)
• Bommie (coral outcrop)
• Cave system diving (overhead environment)
• Drop-off / wall dive
• Fringing reef (close to shore)
• Lagoon (sheltered water inside reef)
• Muck diving (sand, macro critters)
• Pinnacle (submerged peak)
• Swim-through (passage in rock)
• Wreck dive (sunken ship / aircraft)

Techniques & skills

• Back kick (reverse finning)
• BTV — Voluntary Tubal Opening
• Controlled emergency swimming ascent (CESA)
• Frenzel equalization (tongue piston)
• Frog kick (silt-free finning)
• Standard diving hand signals
• Helicopter turn (in-place rotation)
• Mouthfill (freediving equalization at depth)
• Recovery breathing (hook breaths)
• Toynbee equalization (swallow)
• Valsalva equalization