Plain English Meaning
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.
Full 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.
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.