Suppressor
Also known as: silencer
A muzzle device that reduces the sound, flash, and recoil of a gunshot by slowing and cooling escaping gases — an NFA-regulated item.
A suppressor (often called a silencer) threads or mounts onto the muzzle and contains a series of baffles that trap and slow the expanding gases behind a bullet. It doesn't make a gun 'silent' like the movies — it reduces the report by roughly 20–35 decibels, typically bringing it down to hearing-safe levels and softening recoil and muzzle flash.
Suppressors are legal to own in most states but are NFA items: you register with the ATF and pay a $200 tax stamp. Benefits include hearing protection, reduced recoil for faster follow-ups, and being a courteous neighbor at the range. The main downsides are cost, the wait, and added length and weight on the firearm.