APU Regulation
APU means auxiliary power unit.
Also defined in 1 more source
Auxiliary power unit. A small turbine- or reciprocating-engine-powered generator, hydraulic pump, and air pump. APUs are installed in the aircraft and are used to supply electrical power, air, and hydraulic pressure when the main engines are not running.
Guidance: Aviation Maintenance Technician Handbook — Powerplant, p. G-2