Muzzle Device
Any attachment threaded onto the muzzle, including brakes, compensators, flash hiders, and suppressor mounts. It redirects exiting gas to a purpose.
Muzzle device is the umbrella term for whatever is threaded onto the end of the barrel. The family includes the muzzle brake, which vents gas sideways and back to fight recoil and muzzle rise; the flash hider, which disrupts the fireball; the compensator, which steers gas upward; and the mount that lets a suppressor attach.
All of them work by redirecting the jet of high-pressure gas that follows the bullet out. Whatever the device, it has to be installed concentric to the bore, because gas escaping unevenly at the crown can nudge the bullet and hurt accuracy.