Joint Publication 1-02, "DOD Dictionary of Military and Associated Terms" defines retrograde movement as "any movement of a command to the rear, or away from the enemy. It may be forced by the enemy or may be made voluntarily. Such movements may be classified as withdrawal, retirement, or delaying action." From a life cycle logistics perspective, this site will primarily focus on retrograde as the return of military equipment, parts, and materiel back to CONUS, either for repair, refurbishment, refit, RESET, or the completion of the mission.
RESET is described in the 2009 Army Posture Statement.