Plain English Meaning
A radio function that holds two frequencies at once -- the one you're using and the next one you'll need -- and lets you switch between them with one button.
Full Definition
A common pilot term for a radio control feature that lets the user pre-tune a standby frequency alongside the active frequency, then swap the two with a single button press. The active frequency becomes standby, and the standby becomes active.
Context Anchor
Seen in discussions of aircraft electronics, digital equipment, and some avionics systems.
Derivation
Named after the back-and-forth motion of flipping something over and back. The two frequencies trade places each time the button is pressed, just like flipping a coin from one side to the other.
Why Pilots Care
It reduces cockpit workload. A pilot can dial in the next ATC frequency well before the handoff, then swap to it instantly when told to contact the next controller -- no fumbling with numbers during a busy moment.
Analogy
Think of a light switch that can only be up or down. It stays where it is until something moves it to the other position.
Intuition Check
Do not read flip-flop here as a casual change of opinion or a sandal. In aircraft electronics, it means a circuit that holds one of two stable conditions and switches when triggered.
Example Sentence 1
After being told to contact Departure on 124.35, she pre-set it in standby and hit the flip-flop as soon as she was clear of the tower frequency.
Example Sentence 2
Flight computers rely on flip-flops to store binary information for altitude alerts and mode selections.