Plain English Meaning
Extra miles added to where you start your descent because a tailwind is making you cover ground faster than usual. Start down sooner so you don't arrive too high.
Full Definition
An increase to the planned top-of-descent distance to compensate for the higher groundspeed produced by a tailwind during descent. Because a tailwind pushes the aircraft over the ground faster, the descent must be started earlier (further from the destination) to reach the target altitude at the right point.
Context Anchor
Used in descent planning, especially when deciding where to begin descent from a high altitude so the aircraft reaches the target altitude at the planned point.
Why Pilots Care
Prevents arriving at a fix too high or too fast, which can compromise with and increase workload during the .