Definition
A turning force that causes an airplane to rotate about its longitudinal axis (the line running from nose to tail), raising one wing and lowering the other.
Plain English
A force that tries to roll the airplane to one side, lifting one wingtip while dropping the other.
Context Anchor
Seen in discussions of flaps, flight controls, and any condition where lift or drag is not the same on both wings.
Derivation
‘Moment’ in physics means a turning force around a point or axis — from the Latin momentum, meaning movement or motion. A ‘rolling’ moment is simply a moment that produces roll.
Why Pilots Care
Uncorrected rolling moments from flaps or other sources can produce unexpected bank angles and increase pilot workload during critical phases of flight.
Intuition Check
Do not read moment as meaning an instant in time here. In this use, a moment is a turning effect; a rolling moment is a turning effect that tries to bank the airplane.
Example Sentence 1
If one flap extends and the other does not, the uneven lift produces a strong rolling moment toward the wing with less flap.
Example Sentence 2
The pilot applied opposite aileron to counteract the rolling moment induced by full flap deployment in the landing configuration.