Filed En Route Delay

Any of the following preplanned delays at points/areas along the route of flight which require special flight plan filing and handling techniques.
  1. Terminal Area Delay. A delay within a terminal area for touch-and-go, low approach, or other terminal area activity.
  2. Special Use Airspace Delay. A delay within a Military Operations Area, Restricted Area, Warning Area, or ATC Assigned Airspace.
  3. Aerial Refueling Delay. A delay within an Aerial Refueling Track or Anchor.

Source: Pilot Contoller Glossary (PCG)