For every action, there is a reaction with an equal but opposed force. With a gun, the force that pushes the bullet foward also pushes the gun backwards, producing a kickback or recoil.

This tag is used for when recoil is portrayed in some fashion, whether it is portrayed realisticly or exaggeratedly.  Can also refer to similar phenomena not involving a firearm, such as the backlash of a released spring or other stretched object.
recoil