Freediving Glossary: 70+ Terms Every Diver Should Know

Freediving terms can sound like a private language, with abbreviations like CWT, FIM and LMC and words like mouthfill, samba and taravana. This glossary explains more than 70 common freediving words in plain English, sorted alphabetically, so you can look things up before a course or while reading a training plan. Where a term deserves more than two lines, we link to a full guide.

For how the disciplines fit together, see freediving disciplines explained.

A–B: from AIDA to buoy

• AIDA: International freediving federation founded in 1992. It sets competition rules, recognises records and runs an education system.
• Announced performance (AP): The depth, distance or time a competitor declares before a dive.
• Apnea: A pause in breathing. Also used as a name for the sport itself. Sometimes spelt apnoea.
• Barotrauma: Injury caused by a pressure difference between an air space in the body and the water around it, usually in the ears, sinuses or lungs.
• Bifins: A pair of separate fins, one per foot. The standard starting point for freedivers.
• Blackout (BO): Loss of consciousness from low oxygen in the brain. See our guide to shallow water blackout.
• Blood shift: Movement of blood from the limbs into the chest at depth, which helps protect the lungs as they compress.
• Bradycardia: Slowing of the heart rate during a breath-hold.
• Breathe-up: Calm, slow breathing at the surface before a dive. Its job is to relax you, not to flush out CO2.
• Buddy: Your safety partner. One dives, the other watches from the surface, then you swap.
• Buoy: The surface float that holds the dive line and gives divers something to rest on.
• Buoyancy: Whether you float (positive), hover (neutral) or sink (negative).

C: from cards to CWT

• Cards: Competition results. White means a clean dive, yellow means penalties, red means disqualification.
• Carbon fins: Fins with carbon fibre blades. Light and responsive, but pricier and more fragile than plastic.
• CMAS: The World Underwater Federation, founded in 1959. Runs freediving competitions with its own rules and records.
• CNF: Constant weight no fins. A depth discipline using only arm pulls and a breaststroke-style kick.
• CO2 table: A dry training session with fixed breath-holds and shrinking rest periods, building tolerance to carbon dioxide.
• Contractions: Involuntary diaphragm spasms late in a breath-hold, caused by rising CO2. Uncomfortable but normal.
• Counterballast: A line system with a heavy weight that can haul a diver to the surface in an emergency.
• CWT: Constant weight. Finning down and up a line without pulling on it. CWTB is the bifins-only version.

D–E: from dive reflex to exhale dives

• Dive reflex: The automatic response to breath-holding with your face in water: slower heart rate and narrowed blood vessels in the limbs. More in the mammalian dive reflex.
• DNF: Dynamic no fins. Swimming horizontally underwater without fins.
• Dry training: Training out of the water: breath-hold tables, breathing work, stretching and equalisation drills.
• Duck dive: The move from floating at the surface to heading straight down, by folding at the hips and lifting the legs.
• DYN: Dynamic apnea. Swimming horizontally underwater with fins, measured in metres. DYNB is the bifins-only version.
• Equalisation: Adding air to the middle ear and mask to balance the rising water pressure as you descend.
• Eustachian tube: The narrow passage between the back of the nose and the middle ear. Equalising pushes air through it.
• Exhale dive: A dive started after a relaxed exhale instead of a full breath. An advanced training tool, used only under instruction.

F–H: from FIM to hypoxia

• FIM: Free immersion. Pulling yourself down and up the line by hand, without fins.
• Fluid goggles: Goggles filled with water instead of air, with corrective lenses, so there is no air space to equalise.
• Foot pocket: The rubber shoe of a fin. Fit matters more than blade material for comfort.
• FRC: Functional residual capacity, the air left in your lungs after a relaxed exhale.
• Freefall: The phase of a dive, once you’re negatively buoyant, where you sink without kicking.
• Frenzel: An equalisation method using the tongue as a piston with the throat closed. See our Frenzel technique guide.
• Glottis: The opening between the vocal cords. Closing it seals the lungs off from the mouth and nose.
• Hypercapnia: Higher than normal carbon dioxide in the blood. It drives the urge to breathe.
• Hyperventilation: Breathing faster or deeper than your body needs. It delays the urge to breathe without adding useful oxygen. Never do it before a breath-hold.
• Hypoxia: Lower than normal oxygen in the body. Severe hypoxia leads to samba or blackout.

L–M: from lanyard to mouthfill

• Lanyard: A short cord clipping the diver’s wrist or ankle to the line, so they can be pulled up if needed.
• Line: The rope hanging from the buoy, used for orientation, safety and depth.
• LMC: Loss of motor control, also called samba. See samba and LMC for the signs and the buddy response.
• Low-volume mask: A mask with little air inside, so it takes less air to equalise.
• Lung squeeze: Injury to the lungs or airways from pressure at depth, often noticed as coughing blood or chest tightness.
• Mask squeeze: Suction on the face and eyes as the air in the mask compresses. Prevented by breathing a little air out through the nose.
• Molchanovs: A freediving education system and equipment brand associated with Alexey Molchanov, with course levels named Lap and Wave.
• Monofin: A single wide blade holding both feet, used with a dolphin kick.
• Mouthfill: An advanced equalisation technique that stores air in the mouth for use deeper down. See mouthfill equalisation.

N–P: from narcosis to partial pressure

• Narcosis: A dreamy, intoxicated feeling some divers report at depth, caused by gases under pressure.
• Neck weight: A weight worn around the neck, used in the pool and by some depth divers to improve trim.
• NLT: No limits. Descending on a weighted sled and returning by any means, usually a lift bag. Rare and dangerous.
• Nose clip: A clip that seals the nose, freeing your hands and removing the need for a mask on some dives.
• O2 table: A dry training session with fixed rest and increasing breath-holds. Done only on land, lying down.
• One up, one down: The core buddy rule. While one diver is underwater, the other is at the surface watching.
• Open-cell wetsuit: Neoprene with an unlined inner surface that seals against the skin. Needs soapy water or lubricant to put on.
• Packing: Gulping extra air into already full lungs. Advanced, and only with an instructor.
• Partial pressure: The share of total pressure from one gas. Falling oxygen partial pressure on ascent is behind shallow water blackout.

R–S: from recovery breathing to surface protocol

• Recovery breathing: Strong breaths straight after surfacing: a short passive exhale, a quick full inhale, a brief pause with pressure. Also called hook breathing.
• Residual volume (RV): The air that stays in your lungs even after a maximal exhale.
• Reverse block: Air trapped in the ears or sinuses that can’t escape as it expands on ascent.
• Reverse packing: Drawing extra air out of the lungs after a full exhale, used for flexibility training. Only with instruction.
• Safety freediver: A trained diver who meets the diver on the way up and stays with them through the surface.
• Shallow water blackout: Blackout near the surface at the end of a dive.
• Spleen effect: Contraction of the spleen during repeated breath-holds, releasing extra red blood cells into circulation.
• Squeeze: General name for pressure injuries, such as mask, sinus, ear or lung squeeze.
• STA: Static apnea. Floating still, face down, measured in time.
• Streamlining: Holding your body in the shape that creates the least drag.
• Surface interval: Rest time at the surface between dives. It should grow with the depth and length of the dive.
• Surface protocol: In competition, removing facial equipment, giving an OK sign and saying “I am OK” within a time limit.

T–Z: from tag to weight belt

• Tag: A marker collected from the bottom plate of a competition line as proof of depth.
• Taravana: Decompression illness in breath-hold divers after many dives to depth with short rests, a word from the pearl divers of the Tuamotu islands. See decompression sickness and taravana.
• Thermocline: A layer where water temperature drops sharply, felt as a sudden chill on the way down.
• Total lung capacity (TLC): The maximum volume of air your lungs hold after a full inhale.
• Tracheal squeeze: Pressure injury to the windpipe, often linked to tension or neck movement at depth.
• Valsalva: Equalising by pinching the nose and pushing with the chest. Common in scuba, unreliable head-down.
• VWT: Variable weight. Descending with a weighted sled and returning under your own power.
• Warm-up dives: Easy, shallow dives that prepare your ears and body before deeper ones.
• Weight belt: A rubber belt worn on the hips to carry lead, with a buckle that releases quickly.

Putting the vocabulary to work

Nobody learns 70 terms by reading a list once. The words stick when they’re attached to something you’ve felt: the first contraction in a static, the first ear that wouldn’t clear, the first time you watched a buddy surface and checked their face.

Before a course, pick the six terms you’ll meet first (breathe-up, equalisation, Frenzel, one up one down, recovery breathing and blackout) and practise explaining each one out loud to a friend who has never been near a dive line.

Safety: Knowing the words for blackout, samba and squeeze is useful, but recognising them in a real buddy needs in-water training with a certified instructor. Never practise breath-holds in water alone.

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