Suppressor

A suppressor, sound suppressor, sound moderator, or silencer, is a device attached to or part of the barrel of a firearm which reduces the amount of noise and flash generated by firing the weapon.

A suppressor is usually a metal cylinder with internal mechanisms to reduce the sound of firing by slowing the escaping propellant gas. Some of the older designs reduced muzzle velocity, however most of the modern ones will give a little additional velocity.

Battlefield 1942
The suppressor was a default attachment for the Sten in Battlefield 1942: Secret Weapons of WWII.

Battlefield 2
In Battlefield 2 suppressors were on the 3 available pistols: the US's/EU's 92FS, the MEC's MR-444 and the PLA'S QSZ-92 and were available in the Special Forces Kit and the Sniper Kit.

Battlefield: Bad Company
In Bad Company all submachine guns are attached with a suppressor. Two of the sniper rifles, the VSS and the SVU, have a suppressor.

Battlefield: Bad Company 2
All of the Engineer-specific weapons are attached with a suppressor. Also, just as in Bad Company, the SVU and the VSS are both attached with a supressor.

Battlefield 3
In Battlefield 3's multiplayer, the sound suppressor attachment can be attached to almost all of the firearms in-game, except for the two revolvers. Using a sound suppressor will cause minimal damage loss at long range, and reduce bullet velocity though sniper rifles will only experience increased bullet drop and no damage reduction. The added weight of the suppressor at the end of the barrel reduces recoil slightly, but also reduces hip fire accuracy (as mentioned in loading screen tips). It is unlocked through kill progression for primary weapons, and silenced versions of the G17, M9, MP-443, and the G18 by leveling up. The M1911 also has a suppressed variant that can be unlocked by being a Battlefield Veteran or an EA Gun Club member.

Tactical Value
The decrease in sound and removal of muzzle flash can allow a player to use his weapon without fear of the sound of gunfire or the bright muzzle flash giving away his position. Using a suppressor on a Light Machine Gun can give players the advantage of providing heavy suppressive fire on enemies without himself becoming an obvious target.

Negative Aspects
When using a suppresor on a weapon, it lowers the weapons effectivness at longer ranges.

Trivia

 * When you first pick up a suppressed weapon in Battlefield: Bad Company, Haggard shows interest but soon says that "silencers are for girls" as he is more of a loud kind of guy than one to show for stealth.
 * In Battlefield 3, despite shotguns being unable to fit a Suppressor in multiplayer, a 870 MCS is found with one in The Eleventh Hour as the player's secondary weapon.