What does the acronym APU stand for in aviation?

In aviation, the acronym APU stands for Auxiliary Power Unit. An APU is a small engine typically located in the tail section of an aircraft that provides power for various functions while the aircraft is on the ground. This includes supplying electrical power, starting the main engines, and providing air conditioning to the cabin when the main engines are shut down.

The function of an APU is critical for ensuring passenger comfort and operational readiness before takeoff, particularly when the aircraft is on the ground and cannot use its main engines. By using an APU, airlines can reduce the wear and tear on the main engines, conserve fuel, and enhance the overall efficiency of operations.

The other options, while they may relate to aviation in some capacity, do not accurately represent the standard use of the term APU within the industry.