What does APU stand for in aviation terms?

The term APU stands for Auxiliary Power Unit in aviation. This device is crucial for providing power to an aircraft while it is on the ground, particularly when the main engines are not running. The APU supplies energy for systems such as lighting, air conditioning, and other essential services, allowing the aircraft to operate independently from ground power sources.

The use of an APU can greatly enhance efficiency and comfort while an aircraft is parked at the gate or during extended ground operations. It contributes to the overall operational readiness of an aircraft, ensuring that flight crews can effectively prepare for departures without the need to start the main engines prematurely.

In contrast, the other options presented do not accurately reflect standard aviation terminology. Airplane Power Unit as a term is not recognized in the context of aircraft systems. Aerial Performance Utility is also not a commonly used term in aviation or engineering, and Advanced Pilot Usage does not correspond to any specific equipment or system relevant in aircraft operation.