Plain English Meaning
Pushing on the rudder pedal on the same side as the wing that's tilted down in a turn. This forces the nose to swing further into the turn, and combined with opposite aileron it sets up a dangerous stall.
Full Definition
Pressure applied to the rudder pedal on the inside (lower) side of a turn, yawing the airplane's nose toward the lowered wing. In a cross-control stall scenario, applying bottom rudder while holding opposite aileron creates a crossed-control condition that can provoke a sudden stall and rolloff toward the lowered wing.
Context Anchor
Seen in cross-control stall discussions, especially when describing a skidding turn near the ground, such as an overshoot from to .