The Bipod is a 200cc underbarrel attachment, which greatly increases a weapon's accuracy when deployed. You must be prone to deploy the bipod.
When you deploy the bipod, you will always look down the scope, cannot move, and since you are prone, you cannot completely look up or down.
There are three bipods on the skill tree, all costing 2 skill points. One is in the first Skill Tier of Heavy Weapons, one in the Second Skill Tier of Assault and one in the second Skill Tier of Marksman.
The Assault Rifle bipod can be equipped on the underbarrel of every Assault Rifle, and is incompatible with the Foregrip and Grenade Launcher.