Nitrox refers to any gas mixture composed of nitrogen and oxygen; this includes all air mixture between 22% and 99% of oxygen.
Enriched Air Nitrox, (EAN/EANx) Nitrox with an oxygen content above 21%, is mainly used in scuba diving to reduce the proportion of nitrogen in the breathing gas mixture.

Reducing the proportion of nitrogen by increasing the proportion of oxygen reduces the risk of decompression sickness, allowing extended dive times and longer bottom times without increasing the need for decompression stops.

Nitrox is not a safer gas than compressed air in all respects; although its use reduces the risk of decompression sickness, it increases the risk of oxygen toxicity of the lung and CNS.