Plain English Meaning
The point where you are allowed to land on a runway has been moved further down from the actual start of the pavement. You can roll over the earlier pavement when taking off or after landing, but you must not touch your wheels down on it when arriving.
Full Definition
A runway threshold that is located at a point on the runway other than the designated beginning of the runway. The paved area before a displaced threshold is available for taxi, takeoff, and landing rollout, but is not available for the touchdown of a landing aircraft.
Context Anchor
Seen on runway markings, , and during planning.