Plain English Meaning
The switch in the cockpit that turns the airplane's main electrical generator on or off.
Full Definition
A cockpit-mounted electrical switch, usually part of the master switch assembly, that connects or disconnects the alternator from the airplane's electrical system. When on, the alternator can charge the battery and supply electrical power to the aircraft's systems while the engine is running. It is often a split-rocker design, with one half controlling the alternator and the other half controlling the battery.
Context Anchor
Seen during cockpit preflight, engine start, and electrical system checks, often near or combined with the battery or master switch.