What is Scuba?

Scuba (Self-Contained Underwater Breathing Apparatus) is an apparatus utilizing a portable supply of compressed gas supplied at a regulated pressure and used for breathing while swimming underwater. The apparatus is often called "scuba gear", a "scuba system" or simply "scuba". Scuba is also the common name for the sport (also called "diving" or "scuba diving") which uses the apparatus for recreational diving.

Like other acronyms (such as radar) scuba has become such an ubiquitous term for underwater breathing equipment and the recreational sport of deep diving that it is usually written without capitals. Even though it is an acronym it has entered common usage in the English language and may be used as a noun or adjective.

There are two kinds of scuba equipment:

The Aqua-lung is a tank (or cylinder) of compressed gas (usually air or mixture similar to air) which is supplied to the diver through a regulator, which adjusts the pressure of the gas to suit the ambient pressure for comfortable breathing. This kind of scuba system is called "open circuit" because the exhaled gas is released into the water and lost. The open circuit aqua-lung is the most common type of scuba system used by recreational divers.
The Rebreather is also a tank (or cylinder) of compressed gas breathed by the diver through a regulator, but with other mechanisms that recycle the exhaled gas. This kind of scuba system is called "closed circuit". The economy of reusing and recycling exhaled gases allows a diver to remain submerged for longer periods