Plain English Meaning

One wing's flap moves and the other wing's flap doesn't, so the two wings produce different amounts of lift and the airplane wants to roll toward the wing whose flap stayed up.

Full Definition

An abnormal flap condition in which the flaps on one wing extend or retract while the flaps on the other wing remain in a different position, producing unequal lift between the two wings and a strong rolling tendency toward the wing with the lower flap setting.

Context Anchor

Encountered during abnormal or emergency discussions about flap problems, especially during approach, landing, or flap retraction after takeoff.