To clarify Rainboe's post - in my experience the codes used in SITA/dispatch/handling are:-
WCHR - 'simple' wheelchair - can climb/descend steps; walk up jetways, but normally a buggy required for long-distance terminal walking.
WCHS- cannot use steps but OK on jetway, can get in and out of aircraft unaided
WCHC - requires lifting in and out of aircraft and into seat etc. (Sometimes known as 'a lift-off')