Freediving Glossary

AIDA

Association Internationale pour le Développement de l'Apnée, 

In English: The International Association for the Development of Apnea

Apnea

Plainly speaking, the cessation of breathing. In this context it means a breath hold. It is ok to do when you are awake, but it is considered a medical issue when one does it involuntarily during sleep. 

Atmosphere (ATM) 

This refers to the pressure exerted by the atmospheric pressure of the earth. It is referred to in combination at times (or conflated) with hydrostatic pressure (pressure exerted by water)  in the context of diving. 

Bi Fin

The type of diving fins most people are used to seeing, that is, one for each foot. Doesn’t generate as much attention as a mono fin, and is exactly half as cool. See: Mono fin

Boyle’s Law

pv=k 

Where: p(=pressure) X v(=volume) = k(=constant)

Plainly speaking, a pressure exerted by a gas is inversely proportional to its volume.
A practical example of how this plays out would be in the pressure you feel in your ears as you descend or ascend, whether in an airplane, driving in the mountains, or diving. 

A visual illustration would consist of an inflated balloon. At the waters’ surface, it is under the pressure of only the atmosphere. (Which is significant, but we are used to it!) Once you take that balloon under water, it begins to become compressed and smaller in size. That reduction in size is a visual example of the above equation. It will reduce in size proportionately to the pressure exerted on it! You can try this with a sealed, empty water bottle in water by taking it to depth and watching it crumple. Please don’t litter though. See: equalization. 

Constant weight with fins 

A competitive freediving discipline that involves the diver diving to depth with the use of fins. 

Constant weight without fins 

A competitive freediving discipline that involves the diver diving to depth without the use of fins or other propulsion aids. 

Duck Dive

An efficient way to dive into the water from the surface. A properly executed duck dive can carry a diver up to 12’ (approx 3-4m) down with little effort. Basically, a duck dive involves being prone on the surface, then bending down at the waist and letting the momentum carry you down along with a pull of the arms and a kick of your feet (or fins). 

If it looks thrashy, you will expend more effort than you should, and give your dive partner something to tease you about. 

Dynamic with fins 

A competitive freediving discipline that involves the diver swimming underwater for distance with the use of fins. This can get you kicked out of your local pool. What does a record look like? Check this out. 

Dynamic without fins

A competitive freediving discipline that involves the diver swimming underwater for distance without the use of fins. Also done to freak out lifeguards at the gym pool.

Equalization

In the diving world, this refers to the equalization of pressure between your sinus cavity, inner ear, (and mask if you are wearing one) and the pressure outside of those spaces. This is needed due to the increase in pressure your body undergoes as you dive deeper. See: Boyle’s law, Frenzel equalization, valsalva equalization

Free Immersion

A competitive freediving discipline that involves the diver using a line to pull down to depth and back up to the surface. It is ok to be at the end of this rope. 

Frenzel equalization

The method of equalization that freedivers often prefer. This method uses less effort and wastes very little air compared to the typical method used by scuba divers. It is a lot easier to visualize with some pro help, so check this out if you’d like to know more: 

Adam Freediver Teaches Frenzel.

See: equalization, valsalva equalization

Low-volume mask

In contrast to a regular scuba or snorkeling mask, a freediving mask is lower in profile and contains less air space (thus the term “low-volume”), minimizing the amount of air space a diver will need to equalize at depth. They also look pretty cool. 

Mono Fin

What most pelagic species use to propel themselves through water. Also: a fin with one blade used by freedivers. Way cooler than regular fins. See: Bi-fin

PADI

Professional Association of Diving Instructors.
This organization has appropriate, safety-centric based training for scuba and freediving. Though not directly endorsed by or affiliated with PADI, the author is a PAD-certified freediver and scuba diver, and highly recommends taking one of their courses to anyone interested in freediving or scuba so that they can keep to an acceptable standard of safety. Your safety is well worth it, and you will have a more enjoyable experience overall. 

Scuba

Stands for “self-contained underwater breathing apparatus”. Scuba divers are fun to dive down to and swim around when freediving, especially when at a vacation destination where said scuba divers overpaid for tank fills. 

SSI

Scuba Schools International

A diving organization that offers training. The author is not associated with or endorsed by SSI, but highly recommends taking a course from a certified diving professional for anyone interested in freediving (or scuba) to keep to an acceptable standard of safety. Your safety is well worth it! 

Valsalva equalization

The method of equalizing traditionally taught to scuba divers. This involves equalizing using the diaphragm to push air against your inner ear, sinus, etc. Uses more air and effort than Frenzel. See: Frenzel equalization, equalization.