This article needs additional citations for verification. (January 2021)
For most airplanes, clean configuration means simply that the wing flaps and landing gear are retracted, as these are the cause of drag due to the lack of streamlined shape. On more complex airplanes, it also means that other devices on the wings (such as slats, spoilers, and leading edge flaps) are retracted. Clean configuration is used for normal cruising at altitude during which lift, or rise in altitude, is not needed.