Scuba diving

Scuba diving is underwater diving using a self-contained breathing apparatus that supplies breathing gas independently of the surface. It allows divers to move underwater without a surface-supplied air line.

Scuba set: A scuba set combines a breathing-gas supply, regulator, and supporting equipment for underwater use. It is the core equipment that makes independent underwater breathing possible.
Scuba cylinder: A scuba cylinder is a refillable high-pressure vessel that stores breathing gas for a diver. It carries the gas supply that distinguishes scuba from surface-supplied diving.
Recreational diving: Recreational diving is noncommercial scuba diving undertaken for enjoyment, exploration, or training. It is the most familiar setting for ordinary scuba equipment and procedures.
Surface-supplied diving: Surface-supplied diving delivers breathing gas from the surface through a hose or diving umbilical. Unlike scuba, it depends on a gas supply connected to the surface.
Diving regulator: A diving regulator delivers breathing gas from a high-pressure cylinder at a pressure suitable for the diver. It reduces cylinder pressure and supplies gas as the diver inhales.
Breathing gas: Breathing gas is a mixture supplied for respiration, including air and specialized diving mixtures. Scuba equipment carries a breathing gas chosen for the dive's depth and purpose.
Technical diving: Technical diving uses specialized training and equipment for dives beyond recreational limits. Greater depth, duration, or complexity demands advanced gas and decompression planning.
Snorkeling: Snorkeling is surface swimming with a breathing tube that lets a person breathe air above the water. It supports surface breathing but does not provide an independent underwater gas supply.
Buoyancy control device: A wearable inflatable device lets a diver adjust buoyancy and carry a cylinder. It helps control depth and compensate for changing buoyancy underwater.
Hydrostatic pressure: Hydrostatic pressure is the pressure exerted by a fluid at rest, increasing with depth. Water pressure rises during descent and affects gas volumes and the human body.

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