Definition
A communication procedure in which a pilot, unable to reach Air Route Traffic Control Center (ARTCC) directly because of a radio frequency outage or weak signal, contacts a Flight Service Station (FSS) and asks the FSS specialist to pass messages between the pilot and ARTCC.
Plain English
When you can't talk to Center directly, you call Flight Service and they pass your message to Center, then pass Center's reply back to you.
Context Anchor
Seen in instrument procedures for an Air Route Traffic Control Center radio frequency outage, when the normal controller frequency is unusable.
Derivation
Relay comes from Old French relais, meaning a fresh set of horses kept along a route to carry messages onward. The idea is the same here: when one link can't reach the destination, a middle station carries the message forward.
Why Pilots Care
It keeps instrument flight plans moving safely by preserving two-way contact with controllers even when primary radios are down.
Intuition Check
Relay does not mean Flight Service is controlling your flight. It means Flight Service is passing the message between you and air traffic control.
Example Sentence 1
Unable to raise Center on the assigned frequency, the pilot contacted Flight Service and requested a relay via FSS radio to report position and receive further routing.
Example Sentence 2
The pilot received the approach clearance that was relayed via FSS radio after direct center contact was lost.