Plain English Meaning
A remote-controlled switch that lets the master switch in the cockpit turn the battery on and off without running heavy battery cables all the way up to the panel.
Full Definition
An electromagnetic switch in the aircraft electrical system that connects or disconnects the battery from the main electrical bus. When energized by a small control current from the master switch, it closes a heavy-duty internal contact that allows the battery's high current to flow to the rest of the aircraft.
Context Anchor
Seen in aircraft electrical and starting system descriptions, especially when explaining what happens after the battery side of the master switch is turned on.