Plain English Meaning
The exact point at the start of the runway that the approach path is aimed at. The descent path on the approach is built so the aircraft passes over this point at a specific height above the runway.
Full Definition
The Landing Threshold Point (LTP) is the point on a runway centerline at the threshold over which the aircraft on a final approach is intended to cross at a specified height. On RNAV and Baro-VNAV approaches, the LTP is a defined three-dimensional point used as the origin for the final approach glidepath, with a published latitude, , and .