Plain English Meaning
Pushing on the rudder pedal on the same side as the direction you're turning — the side the airplane is leaning toward. In a left turn, that's the left pedal; in a right turn, the right pedal.
Full Definition
Rudder pressure applied in the same direction as the turn — toward the inside (lower wing) of the bank. In a left turn, this is left rudder; in a right turn, right rudder. When applied excessively or out of coordination with aileron, it skids the airplane and is a primary cause of cross-control stalls in the base-to-final turn.
Context Anchor
Seen in cross-control stall discussions, especially when a uses too much rudder in a turn while the bank with opposite aileron.