Definition
An amended routing issued by air traffic control before takeoff that replaces all or part of the route originally filed in the flight plan. It is delivered to the pilot during clearance delivery to manage traffic flow, weather avoidance, or airspace constraints downstream.
Plain English
Before you take off, ATC gives you a different route than the one you filed. You haven't moved yet, but your planned path through the sky has been changed.
Context Anchor
Commonly encountered before an IFR departure when receiving a clearance from clearance delivery, ground control, or an electronic pre-departure clearance system.
Derivation
Pre-departure means before leaving the ground. Reroute means a changed route. Together: a route change given before you depart.
Why Pilots Care
Allows the route to be adjusted on the ground so the flight can depart without delays or conflicts that would otherwise appear once airborne.
Intuition Check
Do not read this as a casual route suggestion. A Pre-Departure Reroute is an ATC-issued change before takeoff, and once accepted it becomes part of the route you are cleared to fly.
Example Sentence 1
Ground gave us a pre-departure reroute, so we held at the gate for a few minutes to load the new waypoints into the FMS.
Example Sentence 2
Because of heavy departure traffic, the crew accepted a pre-departure reroute that lengthened the flight by fifteen minutes but avoided holding.