A Hold-Down and Release Mechanism (HDRM) is an equipment on a spacecraft used to hold a part in a fixed position, and release when commanded.

The purpose of an HDRM is to hold an equipment on a spacecraft (e.g. a solar panel) securely in place during part of the mission to prevent unintentional movement, or release, before it's deployment.

For example, a solar panel needs to be held securely during launch to prevent potentially catastrophic radiation damage, but it also needs to deploy and rotate freely when in use. An HDRM is used to hold it place, and release it when commanded.

Pyrotechnic HDRMs use a small explosive charge to trigger the separation (e.g. frangible-nuts), but these are increasingly replaced with non-pyrotechnic devices using either a solenoid to actuate a latch, or a small electric motor.