Definition
An electrical relay that, once energized by a brief input signal, keeps itself energized through its own contacts until a separate command interrupts the circuit. It maintains, or 'holds,' a switched state without requiring the original triggering signal to remain active.
Plain English
A switch that latches itself on after a quick push and stays on until something tells it to turn off.
Context Anchor
Seen in aircraft electrical-system descriptions, wiring diagrams, and maintenance troubleshooting, especially where a momentary switch starts a circuit that must remain on.
Derivation
From 'hold' meaning to keep in place, and 'relay' from the Old French relais, originally a fresh team of horses kept ready to take over a journey. In electrical use, a relay is a device that takes a small signal and uses it to control a larger circuit. A holding relay is one that keeps the circuit it controls in place after the signal has gone.
Why Pilots Care
Many cockpit switches give only a brief signal; the holding relay is what keeps the system running afterward. Knowing this helps a technician troubleshoot faults where a system energizes momentarily and then drops out, which usually points to the relay failing to hold rather than the original switch.
Analogy
Like a doorbell that, once pressed, keeps ringing until someone presses a second button to stop it, instead of ringing only while the first button is held down.
Intuition Check
Do not read holding as physically gripping a part. In this term, holding means keeping an electrical circuit on after the original control input is released.
Example Sentence 1
When the technician traced the fault, he found the holding relay was not latching, so the fuel pump shut off the moment the start switch was released.
Example Sentence 2
During preflight checks the technician verified that the holding relay would not drop out under vibration.