Oxygen deficiency occurs when the level of oxygen in the air or in the body is lower than normal. This can happen in high altitudes, where the air pressure is reduced, or in enclosed spaces with poor ventilation. The body relies on oxygen for essential functions, and a lack of it can lead to symptoms like shortness of breath, confusion, and fatigue. In severe cases, oxygen deficiency can result in serious health issues, including loss of consciousness or even death. It is important to monitor oxygen levels in environments such as aircraft, submarines, or mines to ensure safety and prevent accidents related to low oxygen availability.