The proper term for a silencer, a cylindrical or occasionally rectangular device that attaches to the end of a firearm or is sometimes built into it, to "suppress", or reduce the sound signature of the
muzzle blast, thus making the weapon significantly quieter. Requires
subsonic ammunition for proper sound reduction. The device itself consists of a tube that attaches to the weapon, usually by threads or a fast-attach device and has any number of designs of
baffles, ballistic wipes or mesh to trap and disperse the hot expanding gas, so that it is at a much lower pressure when it leaves the unit, which reduces noise signature and flash. Often, water, lithium grease or
coolant are added to "wet" suppressors, to make quieter by further cooling the gases. Revolvers can't be suppressed, but many semi-automatic handguns and most rifles can, with the proper barrels, tuning and ammunition.
Common tool for special operations personnel and assassins for covert elimination of enemies or targets, government agents and SWAT teams for raids, hunters in Europe for
noise control and American
ranchers and civilian hobbyists who pay a $200
BATFE tax stamp. Popular with more sophisticated criminals as well, who obtain or produce them illegally.