Plain English Meaning
After your wheels touch down in a crosswind, the wind can suddenly lift the wing on the windward side. You need to keep turning the control wheel into the wind on the rollout to stop that from happening.
Full Definition
A crosswind landing condition in which one wing lifts after the wheels are on the runway because the crosswind, striking the upwind side of the airplane, gets under that wing and rolls it upward. If the pilot does not promptly add aileron deflection into the wind to hold the wing down, the airplane can be tipped, weathervaned, or even rolled onto the downwind wing.
Context Anchor
Encountered during , especially just after the touch down and during the .