Plain English Meaning
Pushing on the right rudder pedal with your foot to keep the airplane's nose pointing straight (or to swing it to the right). In most propeller airplanes, the nose naturally wants to drift left when you add power or pitch up, so the pilot pushes on the right pedal to stop that drift.
Full Definition
Application of force on the right rudder pedal to deflect the rudder to the right, yawing the aircraft's nose to the right. In single-engine propeller airplanes, right rudder pressure is used to counteract the left-turning tendencies caused by torque, P-factor, spiraling slipstream, and , particularly during -power, -, and high--of-attack .