Bipod

Bipods are an attachment typically reserved for use on light machine guns or sniper rifles, although it's possible to equip them on assault rifles and carbines. They allow the user to provide more accurate fire from a stabilized position while prone or from a raised surface.

Battlefield 3
"Bipods allow the shooter to Support their gun on flat horizontal surfaces, or when prone, to gain an increased accuracy and reduced recoil. By default, Aiming will enter Supported Shooting."

- Battlelog description

In Battlefield 3, the Deployable Bipod is an attachment for light machine guns, sniper rifles, carbines, (excluding the AKS-74u, the G53, the A-91, and the QBZ-95B) and assault rifles. It is featured in both the Singleplayer campaign and in Mulitplayer.Light machine guns are initially equipped with this attachment.

Singleplayer
Several weapons found in the Singleplayer campaign have a Bipod attachment;
 * An M249 in the mission, Operation Swordbreaker
 * An enemy RPK-74M in the mission Operation Swordbreaker
 * An M98B in the mission, Operation Guillotine

Multiplayer
The bipod is unlockable for almost all weapons (excluding secondaries, Personal Defense Weapons, equipment, the AKS-74u, A-91, G53, and the QBZ-95B) in Multiplayer mode.

The bipod is deployed by aiming near the cover or ground you wish to deploy it on and it will automatically activate. The bipod only deploys on something that is chin high, after a patch. This takes just over a second, but provides an instant boost to the accuracy of the weapon with the bipod, as well as decreasing felt recoil. The recoil when using a bipod will significally increase when suppressed. It remains deployed only for as long as the player remains stationary, and limits the radius in which the player can aim the weapon. It is possible, however, to override bipod deployment by simply continuing to move while going into sight mode. There are several glitches associated with the bipod, such as a tendency to deploy in unusual locations when near a wall, making it difficult or impossible to fire accurately.

Trivia

 * In the beta of Battlefield 3, the bipod was useable on the AKS-74u, however, upon release, this feature was removed.
 * When using the bipod in conjunction with scoped optics (the 12x Ballistic scope for example), the scoped view will have a larger radius than when not using the bipod.