An APU (Auxiliary Power Unit) refers to a device that generates electrical power and sometimes also compressed air for an aircraft when it is on the ground. It is typically located in the rear of the aircraft, in the tail section, and is used to provide necessary power for a range of systems, including air conditioning, lighting, and engine starting. The APU operates independently of the main engines and is usually a small gas turbine engine. Its purpose is to ensure the functionality and comfort of the aircraft when the main engines are not running or not required to be operational.
