A measurement of how much air a diver uses at a specific depth. Used for planning dive time and tank usage.

An inflatable vest worn by divers that allows control of buoyancy underwater and on the surface.

The total time a diver spends underwater from descent to the beginning of ascent.

Proof that a diver has completed a scuba course and met training standards (e.g., SSI, PADI, NAUI). 

A preliminary dive used to assess a diver's skills and equipment before further diving, often required on liveaboards.

A digital device that monitors depth, time, ascent rate, and calculates safe decompression limits.

A professional-level diver certification that qualifies individuals to supervise diving activities and assist instructors.

A breathing gas with a higher oxygen content than regular air (usually 32–36%). Reduces nitrogen absorption and allows longer bottom times.

The process of balancing pressure in the ears and sinuses during descent to prevent discomfort or injury.

Underwater diving without the use of breathing apparatus, relying on holding one's breath.

The part of the regulator attached to the tank valve that reduces tank pressure.

An instrument that measures tank pressure, depth, or both.

A common method for entering the water from a dive boat or platform.

A dive boat that includes sleeping quarters, meals, and multiple days of diving—ideal for remote dive sites.

Damage caused by holding breath during ascent, can be life-threatening; emphasizes the importance of continuous breathing.

The maximum time a diver can spend at a depth without requiring decompression stops during ascent.

A rubber seal used on scuba tanks and regulators to prevent leaks.

Popular dive certification agencies. PADI (Professional Association of Diving Instructors) offers global training standards and certifications.

A structure made of coral or rock in shallow water, often home to a variety of marine life and a popular dive site.

A device that delivers air from the tank to the diver, allowing normal breathing at various depths.

A 3-minute stop at 5 meters (15 feet) during ascent to allow excess nitrogen to safely leave the body.

The amount of time a diver spends on the surface between dives to allow nitrogen to be eliminated from the body.

A preliminary dive used to assess a diver's skills and equipment before further diving, often required on liveaboards.

A high-pressure cylinder containing compressed air or nitrox used for breathing underwater.  Can be steel or aluminum. 

A diver's position in the water. Good trim means a horizontal, streamlined position for better control and efficiency.

The practice of using a compass or natural references to find your way underwater.

How far you can see underwater, often affected by particles, plankton, or weather.

A neoprene suit worn by divers to provide thermal insulation in colder water.

A belt with lead weights used to offset the buoyancy of the wetsuit and body, allowing easier descent.