Plain English Meaning
Pushing on the rudder pedal on the side you're turning toward. If you're turning left, it's the left pedal; turning right, it's the right pedal.
Full Definition
Pressure applied to the rudder pedal on the inside of a turn — that is, the rudder pedal on the same side as the direction the airplane is turning. In a left turn, inside rudder is left rudder; in a right turn, inside rudder is right rudder. Excess inside rudder pressure during a turn produces a skidding turn and is a key ingredient in the cross-control stall.
Context Anchor
Seen in discussions of skidding turns and cross-control stalls, especially when turning from base toward final approach.