1. a flap that is located on the under surface of the trailing edge of an aircraft wing and that splits away from the wing structure when rotated downward, producing an increase in lift or drag or both. Cf. landing flap.
2. a flap that is located on the upper surface of the trailing edge of an aircraft wing and that acts as a spoiler when rotated upward.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.