Plain English Meaning

The airplane is bouncing or rocking, and the pilot's own control inputs — meant to fix it — are actually making it worse because each correction comes a moment too late and ends up adding to the next bounce.

Full Definition

A series of unintended up-and-down (or other) oscillations of the airplane caused by the pilot's own control inputs, where each correction is applied out of phase with the airplane's motion and amplifies rather than dampens it. In landing, this typically appears as repeated nose-up/nose-down bouncing as the pilot chases the airplane's pitch attitude with the elevator.

Context Anchor

Seen in landing discussions, especially when a bounced landing or porpoise gets worse because the pilot keeps making control corrections at the wrong time.