SCUBA

Self contained underwater breathing apparatus,

Scuba diving ("SCUBA" originally being an acronym for self contained underwater breathing apparatus, now widely considered a word in its own right)^[1] is a form of underwater diving in which a diver uses a scuba set to breathe underwater.^[2]

Unlike early diving, which relied exclusively on air pumped from the surface, scuba divers carry their own source of breathing gas (usually compressed air),^[3] allowing them greater freedom than with an air line. Both surface supplied and scuba diving allow divers to stay underwater significantly longer than with breath-holding techniques as used in snorkelling and free-diving.

According to the purpose of the dive, a diver usually moves underwater by swimfins attached to the feet, but external propulsion can come from an underwater vehicle, or a sled pulled from the surface.