Definition
The act of extending or retracting the wing flaps, which changes the wing's lift and drag characteristics and produces noticeable pitch and airspeed changes that the pilot must anticipate and correct with elevator and power adjustments to maintain straight-and-level flight.
Plain English
Moving the flaps down or back up. Whenever you do this, the airplane wants to pitch up or down and the airspeed shifts, so you have to adjust the controls to keep flying level.
Context Anchor
Seen during instrument straight-and-level flight, approaches, and any checklist or procedure that calls for changing flap position.
Derivation
Flap comes from an old word meaning to strike or move back and forth. That helps because an airplane flap is a movable part of the wing. Operation comes from Latin words meaning work or action; here it means the action of using the flaps, not just the flap itself.
Why Pilots Care
Correct flap operation lets the pilot reduce airspeed or increase descent rate without large pitch changes that could disturb instrument flight.
Intuition Check
Do not think of flap operation as only moving a handle or switch. In flight, it includes managing what the airplane does after the flaps move.
Example Sentence 1
During flap operation on final approach, the pilot anticipated the nose-down pitch tendency and adjusted elevator pressure to hold the glide path.
Example Sentence 2
Before entering the approach, the pilot verified proper flap operation using the cockpit indicator.