Plain English Meaning
A paved or prepared strip of ground just past the end of the runway, set aside as a safe place for an airplane to roll out and stop if the pilot has to abort a takeoff.
Full Definition
An area beyond the takeoff runway, no less wide than the runway and centered on its extended centerline, designated by the airport authority as suitable for an aircraft to decelerate and stop during a rejected takeoff. A stopway is able to support the airplane's weight during a rejected takeoff but is not used for normal takeoff or landing operations.