Plain English Meaning
A precise GPS point sitting right at the start of the landing portion of the runway. The aircraft's navigation system uses it as the spot where, if you can't see the runway, you must go missed.
Full Definition
A named GPS/RNAV waypoint located at the beginning of the landing surface of a runway, used as the missed approach point on most RNAV (GPS) approaches with vertical guidance and as a reference for the final approach segment.
Context Anchor
Seen on RNAV instrument approach charts at the runway end, commonly as the last named point on the before the .