Diving glossary for beginners

The words you will read on our pages and hear at the dive centre, explained in plain language.

Levels and training

Discovery dive: A first, shallow dive with an instructor, without any certification. You learn a few basic skills and the instructor stays right next to you the whole time.Where to learn to dive
Open Water: The first full certification (PADI and SSI Open Water, CMAS 1 star). It lets you dive with a buddy down to about 18 m. The French equivalent, FFESSM Niveau 1, allows 20 m with a guide.Open Water dive sites
Advanced Open Water: The next step after Open Water: a few training dives (usually deep and navigation, plus others you choose) that extend your limit to about 30 m.Dive sites for Advanced divers
Deep Diver: A specialty that trains you to dive down to 40 m, the usual limit of recreational diving. In France, Niveau 3 (FFESSM) covers deep autonomous diving.Sites for experienced divers
Technical diving: Diving beyond recreational limits: deeper than 40 m, with planned decompression stops, special gas mixes or rebreathers. It needs dedicated training and equipment.Technical dive sites
Divemaster / dive guide: A professional who leads certified divers underwater: briefing, navigation, spotting marine life and watching over the group. Not an instructor: a divemaster doesn't teach courses.
Check dive: An easy first dive that many dive centres ask for, to see how you handle buoyancy and your gear before taking you to harder sites. Normal, especially after a long break.Level up: train before you go
Logbook: Your record of past dives: date, site, depth, time. Dive centres often ask how many dives you have logged, and when your last dive was.

Safety and physiology

Buddy: The diver you pair with. You check each other's gear before the dive and stay close enough to help each other underwater.
Dive group: The divers who go down together with the same guide. In France it is called a palanquée, a word you will hear in French-speaking dive centres.
Equalising: Balancing the pressure in your ears as you go down, usually by pinching your nose and blowing gently. Do it early and often; never force it.
Safety stop: A pause of about three minutes at around 5 m at the end of every dive, to let your body release nitrogen before you surface.
No-decompression limit: The longest time you can stay at a given depth and still go straight up (with just a safety stop). The deeper you are, the shorter it is. Your dive computer shows it.
Decompression stop: A required stop on the way up when you have stayed beyond the no-decompression limit. Planned decompression belongs to technical diving.
Ascent rate: How fast you come up. Slowly: most dive computers ask for about 9–10 m per minute and warn you if you go faster.
Nitrogen narcosis: A drunk-like effect of nitrogen under pressure, often noticeable from around 30 m. It fades as you go shallower. One reason deep diving needs training.
Surface interval: The time spent at the surface between two dives. Your dive computer uses it to plan how long you can stay down on the next dive.
Nitrox: Air with more oxygen, often 32% or 36%. Less nitrogen means longer no-decompression time at moderate depth, but a shallower maximum depth. It needs a short certification.

Gear

BCD: The buoyancy control device: the jacket that holds your tank and that you inflate or deflate to float, sink or hover.
Regulator: The part you breathe from: it lowers the tank pressure to a breathable pressure. It comes with a spare mouthpiece (the octopus) for your buddy.
Dive computer: A wrist computer that shows your depth, time, no-decompression limit and ascent speed. Today most divers, and many dive centres, rely on it.
Wetsuit thickness: Wetsuits are sold by thickness in millimetres: 3 mm for warm water, 5 mm or 7 mm for cooler water. Each destination page gives the water temperature.
Drysuit: A sealed suit that keeps you dry, worn with warm layers underneath in cold water (Norway, Scotland, Canada…). It needs its own short training.
SMB / DSMB: A surface marker buoy: an inflatable tube you send up at the end of a dive so boats know where you are. Essential on drift dives.
Reef hook: A hook on a short line that you place on dead rock to stay put in a strong current and watch the action without holding on to coral.

On the dive

Buoyancy: Whether you float, sink or hover. Good buoyancy (hovering without effort) protects the reef, saves air and is the skill that most improves your dives.
Shore dive: A dive you start by walking into the water from a beach, jetty or rocks, without a boat.
Giant stride and back roll: The two usual ways to get in from a boat: a big step forward from a high deck, or rolling backwards from the side of a small boat.
Liveaboard: A boat you live on for several days, diving three or four times a day. Often the only way to reach remote sites (Similan, Cocos, Socorro…).
Current: Water moving along the site. Mild current is pleasant; strong current needs experience, a guide who knows the tides and good air management.
Drift dive: A dive where you let the current carry you along the reef and surface away from where you started; the boat follows your marker buoy.Drift dives
Slack tide: The short calm between two tides when the current slows or stops. Many current-swept sites are dived at slack.
Visibility: How far you can see underwater, in metres. It changes with plankton, rain, swell and season.
Thermocline: A sharp change in water temperature at a certain depth: you feel it as a sudden cold layer, often with a blurry line in the water.

Types of dive sites

Reef, pinnacle and bommie: A reef is a structure built by corals. A pinnacle rises from deep water towards the surface; a bommie is a small isolated coral head on sand.Reef and pinnacle dives
Wall: A reef that drops almost vertically into deep water. Easy to go deeper than planned: keep an eye on your depth.Wall dives
Wreck and penetration: A sunken ship, plane or vehicle. Swimming around it is open water; going inside (penetration) is an overhead environment that needs specific training.Wreck dives
Overhead environment: Any place where you can't swim straight up to the surface: caves, caverns, inside wrecks, under ice. Only with the matching training.
Cavern and cave: A cavern is the part of a cave where daylight from the entrance is still visible. Beyond that, cave diving needs full cave training.Cave, cavern and cenote dives
Cenote: A natural sinkhole filled with fresh water, typical of Mexico's Yucatán, often opening onto caverns with beams of light.Cave, cavern and cenote dives
Blue hole: A deep, round sinkhole in a reef or in the sea floor, dark blue when seen from above.
Muck diving: Diving on sand, silt or rubble that looks empty but hides rare small creatures: frogfish, nudibranchs, seahorses, mimic octopus.Muck and macro dives
Artificial reef: A structure sunk on purpose (ship, sculptures, concrete blocks) so that corals and fish settle on it, and to take pressure off natural reefs.Artificial reefs and underwater art

Marine life words

Macro: Small marine life, often a few centimetres long: nudibranchs, shrimps, pygmy seahorses. Divers go slowly and look closely.Where to see macro life
Pelagic: Animals of the open sea rather than the reef: sharks, manta rays, tuna, big schools. Often seen on blue-water or current dives.Blue water and big animal dives
Cleaning station: A spot on the reef where small fish and shrimps clean larger animals. Mantas and sharks come back to it, so divers wait nearby without blocking it.
Nudibranch: A colourful sea slug, often only a few centimetres long. A favourite of underwater photographers.

General definitions that apply whatever your training agency. The limits quoted are those of the most common courses: your instructor and your agency always have the final word. See how agencies compare.