Plain English Meaning

An electric motor runs off the battery and spins the engine fast enough to start it. When the engine catches and speeds up, the motor disconnects on its own.

Full Definition

A starting system in which an electric motor, powered by the aircraft battery, turns the engine crankshaft directly through a small pinion gear that engages a ring gear on the engine. When the pilot activates the starter switch, the motor spins the crankshaft fast enough for the ignition system to fire the spark plugs and the engine to start. Once the engine starts and exceeds the cranking speed, the pinion automatically disengages from the ring gear.