Scuba diving is the term used to describe the use of a self-contained breathing set to stay underwater for periods of time greater than the average individual can breath-hold. The diver carries all equipment necessary for diving and is not reliant upon equipment elsewhere (e.g. on the surface) to supply breathing gas or other support during the dive. The diver swims underwater using fins attached to his/her feet. Some divers also move around with the assistance of a DPV (Diver Propulsion Vehicle), commonly referred to as a "scooter", or by using surface-tethered devices called sleds, which are pulled by a boat.
The word 'SCUBA' is an acronym for "Self Contained Underwater Breathing Apparatus", but it has become acceptable to refer to 'scuba equipment' or 'scuba apparatus'. The term SCUBA in common usage usually means open-circuit equipment in which gas (usually air) is breathed from a tank of compressed gas and then exhaled into the water, usually in the line of kit development started by Emile Gagnan and Jacques-Yves Cousteau. But rebreathers (both semi-closed circuit and closed circuit) are also self-contained systems and could be classed as SCUBA. The term SCUBA arose during World War II and originally meant USA combat frogmen's oxygen rebreathers.