Plain English Meaning
A small electric switch that uses a magnetic coil to flip a much bigger switch, allowing a strong burst of electricity from the battery to reach the starter motor and crank the engine.
Full Definition
An electromagnetic switch in the aircraft starting circuit that, when energized by the pilot turning the ignition key or pressing the start switch, closes a heavy-duty contact to send high current from the battery to the starter motor.
Context Anchor
Seen in engine starting system descriptions, especially when tracing how moves from the battery to the starter motor during engine start.