Plain English Meaning
The two pedals at your feet that swing the airplane's nose left or right. Push the left pedal, the nose swings left; push the right pedal, the nose swings right. On the ground these same pedals usually steer the airplane and, by pressing the tops, apply the brakes.
Full Definition
One of two foot-operated controls in the cockpit, mounted on the cockpit floor, that the pilot uses to deflect the rudder left or right and thereby control yaw — the side-to-side movement of the airplane's nose around its vertical axis. On most airplanes the rudder pedals also operate the nosewheel or tailwheel steering for ground handling, and the upper portion of each pedal applies the brake on the corresponding main wheel.