relay

1. Communications: Fixed station (such as an earth station) or a mobile station (such as a satellite) that receives signals and rebroadcasts them at the same or a different frequency, to extend the broadcast's reach. See also repeater.

2. Electronics: Device with two separate circuits or coils, in which current in one coil controls a much larger (or higher voltage) current in the other coils. Relays work as switches, and are used often in an engine or motor startup applications.