As with any sport, or new activity that you get into, you'll find that freediving has a number of terms that you might be unfamiliar with at first. More so since many are simple acronyms with no real hint of their meaning. Here is a list of some of the most common terms you'll run into when browsing freediving blogs or forums:
Let's start with the disciplines. There are six official competition disciplines (three in the pool, and three in open water), and two that are for world record only.
Static (STA): Static apnea is where the diver attempts to hold his or her breath for as long as possible while their respiratory tracts are immerged in water. This is also the only discipline which measures the duration of the dive over the distance.
Dynamic (DYN): Dynamic apnea is what we've all tried since we were kids, trying to see how far you could swim in a pool on a single breath. DYN allows divers to use long fins or a monofin for propulsion.
Dynamic No Fins (DNF): DNF is also concerned with the distance the diver is able to cover in a pool, though all propulsion aids are prohibited. This requires that the diver have excellent technique in their underwater swimming form.
Free Immersion (FIM): In free immersion diving, the diver dives as deep as possible without the use of propulsion equipment, but instead by pulling on the rope during their descent and ascent. This is a fantastic way to both warm up, as well as practice equalization as the diver can very easily control their rate of descent.
Constant Weight (CWT): The freediver descends and ascends by using his or her fins and/or arms without the use of the rope or changing their ballast (thus the name) during the dive. CWT is perhaps the most common form of freediving in competition, and also most closely resembles what you do while snorkeling.
Constant Weight No Fins (CNF): The freediver uses only his or her muscle strength to achieve great depths without the use of propulsion equipment or the rope to assist their dive. Many freedivers consider this discipline to be the most pure form of freediving.
Variable Weight (VWT): In VWT the diver is able to descend using a ballast weight to get them to depth as quickly as possible, and then ascents under his or her own power, using arms and/or legs, as well as pulling on the rope. This style was made famous in Lec Besson's “Le Grand Bleu.”
No Limits (NLT): As the name implies the diver has no limits to what they are able to use in their descent or ascent to get as much depth as quickly as possible. Often done by descending on a sled similar to VWT, and then ascending with the use of a balloon.
Now that we know the different types of diving, let's move into some more general freediving terms.
Black Out (BO): this occurs when the diver looses consciousness due to hypoxia, or low oxygen (O2) levels. This can happen after a very long Static, or due to what is commonly known as a Shallow Water Blackout.
Shallow Water Blackout (SWB): happens due to the change in partial pressure of O2 in your blood during the ascent of your dive. See Dalton's Law. After discussing SWB with some other instructors we realized that Shallow Water Blackout is a misnomer as technically a BO during a static is in shallow water, but is not caused by the changes in partial pressure. We found that Ascent Induced Blackout (AIB) is much more accurate.
Loss of Motor Control (LMC): Before a blackout, but at the end of a dive, the diver, being very low on O2 may experience an LMC. The diver often doesn't notice that this happens, which is yet another reason that a buddy is so important. LMC is often fondly referred as a 'samba' as it's as if the diver were dancing (though with much less grace).
In a competition, where you're most likely to to see BO and LMC, you'll also run into a few specific competition terms.
Official TOP: This refers to the official Time Of Performance. Competitions are on a very specific schedule, and divers are given an exact TOP for when their dive is to commence.
AP / RP: Along with a specific TOP divers must give their Announced Performance before a competition, and whatever they are able to achieve is referred to as their Realized Performance.
PB: is a diver's Personal Best. This comes up almost any time you get two divers together discussing their progress.
Mammalian Dive Response (MDR): MDR refers to the amazing physical changes your body undergoes to help you dive longer and safer at depth. One common mistake is that people will use the word 'reflex' over 'response.' A reflex is more simple, one input to one output. Think about the test that the doctor does when testing the reflex of your knee/leg. Whereas a response is much more complex, which is exactly what MDR is.
FRC dives: FRC dives are often used when training, and refers to diving at Functional Residual Capacity, which is basically an exhale dive. Please be careful with FRC dives unless you know what you're doing (yet another reason to take a course).
Duck Dive: A good duck dive is very important for every dive. Sometimes referred to as the 'entry' (mostly in places like Hawaii where surfing is much more common), a good duck dive will get the diver a few meters underwater nearly instantly and comfortable, as well as putting them into a good streamline body position.
apnea vs. freediving vs. free diving: Officially the sport is apnea. Even look at what AIDA stands for: Association Internationale pour le Développement de l'Apnée (International Association for the Development of Apnea). In common parlance freediving is how nearly everyone refers to it. However, recently I've seen 'free diving' (with the space) quite a bit, which is less correct. Though understandable, every piece of freediving literature that I've seen does not use the space.