Plain English Meaning
Pushing the rudder pedal all the way in the opposite direction the airplane is spinning, and holding it there hard until the spinning stops.
Full Definition
A spin-recovery action in which the pilot applies and holds full rudder opposite the direction of rotation to stop the yawing motion that sustains a spin. The rudder is held firmly against its stop until rotation stops, after which the elevator is used to break the stall and recover from the resulting dive.
Context Anchor
Seen in stall and spin awareness training, especially when discussing how to stop yaw before a stall develops into a spin.