Plain English Meaning
It's the point on a GPS approach where, if you can't land, you must start the go-around procedure.
Full Definition
On a GPS instrument approach, the Missed Approach Waypoint (MAWP) is the specific point in the GPS navigation database that defines where the missed approach procedure begins. If the pilot has not seen the runway environment and decided to land by the time the aircraft reaches this waypoint, the missed approach must be initiated. The MAWP is normally located at or near the runway threshold and is sequenced automatically by the as part of the published approach.