Definition

Used by Air Traffic Control (ATC) to delay an aircraft for traffic management reasons; i.e., weather, traffic volume, etc. Hold-for-release instructions (including departure delay information) are used to inform a pilot or a controller (either directly or through an authorized relay) that an IFR departure clearance is not valid until a release time or additional instructions have been received.

(As defined by the U.S. Federal Aviation Administration's Aeronautical Information Manual, Pilot/Controller Glossary.)