A silencer, also known as a sound suppressor, suppressor or sound moderator, is a muzzle device that reduces the acoustic intensity of the muzzle report (sound of gunfire) and eliminates muzzle flash when a gun (firearm or air gun) is discharged, by modulating the speed and pressure of the gas ejection from the muzzle and hence suppressing the muzzle blast. Like a muzzle brake, a silencer can be a detachable accessory mounted separately onto the muzzle, or an integral part of the barrel.
A typical silencer is a metal cylinder with internal sound baffles that slow and cool the escaping propellant gas, dissipating its kinetic energy over a longer time and over a larger area, thus reducing the blast intensity and decreasing both the sound volume and recoil impulse generated during shooting. A flash suppressor, on the other hand, specifically cools or disperses burning gases which typically already exited the muzzle of a carbine-length weapon to reduce the amount of flash, without reference to sound reduction.
In most countries, silencers are regulated along with firearms. For civilian use, they are often tightly controlled, or banned entirely.