Plain English Meaning
A stall caused by using the rudder and ailerons against each other -- a setup that most often happens when a pilot turning onto final tries to fix an overshoot by stepping on the rudder to swing the nose around while holding the wings from banking too steeply. At low speed this can flip the airplane into a stall before the pilot expects it.
Full Definition
A stall that occurs when the airplane is flown with the ailerons deflected one way and the rudder deflected the opposite way, typically during the base-to-final turn when a pilot uses opposite aileron to limit bank while holding inside (bottom) rudder to tighten the turn. The resulting skid combined with can produce a sudden, in which the lower drops sharply and the airplane rolls toward the inside of the turn, often with little warning and at low .