Plain English Meaning

When an airplane is flying very fast, moving the control wheel to roll one way can actually make the airplane roll the other way, because the force on the aileron twists the wing instead of just tilting the airplane.

Full Definition

A high-speed aerodynamic condition in which deflecting an aileron produces a roll in the opposite direction to that intended. At high airspeeds, the aerodynamic load created by the deflected aileron twists the wing itself, changing the wing's angle of attack enough that the wing's reaction overpowers the aileron's own lift change, reversing the rolling moment.

Context Anchor

Seen in high-speed flight and discussions, especially when explaining speed limits and why must be stiff enough to resist twisting.