Definition
An electrically operated switch in which a small control current energizes an electromagnet, which in turn opens or closes a separate set of contacts carrying a larger current. Relays allow a low-power circuit (such as a cockpit switch) to control a high-power circuit (such as a starter motor or landing light) safely and remotely.
Plain English
A small electric switch that uses a tiny bit of power to flip a much bigger switch on or off. The pilot's switch sends a low signal; the relay does the heavy work of connecting the high-current circuit.
Context Anchor
Seen in aircraft electrical system descriptions, wiring diagrams, and maintenance troubleshooting for items such as lights, pumps, and starters.
Derivation
From the Old French 'relais,' meaning a fresh set of horses kept ready to take over from tired ones along a route. The electrical relay works the same way — a small incoming signal hands off the work to a fresh, stronger circuit waiting to do the heavy lifting.
Why Pilots Care
Relays allow cockpit switches to safely control high-power devices without running heavy cables through the flight deck.
Analogy
Think of a relay like a remote light switch: a small button controls a powerful lamp without carrying the full current through the button itself.
Intuition Check
Do not think of a relay as a race handoff or a radio rebroadcast here. In an aircraft electrical system, a relay is a switch operated by electricity.
Example Sentence 1
When the pilot pressed the starter switch, the starter relay closed and sent battery power to the starter motor.
Example Sentence 2
A worn starter relay prevented the engine from cranking even though the battery was fully charged.