The clip point BAYONET is a battlefield classic. Originally intended to be mounted on your rifle so you could use it as a spear, this baby rides in your pocket instead and comes out when you start wielding CQB-style.
The Bayonet Knife is a melee weapon in PAYDAY 2 that was introduced through the Gage Assault Pack DLC. It becomes available to all players who have reached level 14 and own the DLC.
The Bayonet Knife is a rifle bayonet detached from its companion weapon and is used as a knife. It is less concealable, deals less uncharged damage and has a somewhat lesser knockdown capability when compared to the other knife included in the DLC, the X-46 Knife, but deals more damage when fully charged.
Bayonets are usually attached to rifles - whilst one can be used as a simple slashing knife, a bayonet's intended usage is that of a stabbing weapon. Some are specifically-designed to be used in conjunction with the (weight of the) rifle they are attached to to build up the amount of kinetic energy needed to effectively strike, and thus on their own are poorly balanced and are not intended to be used as such.
This particular knife seems to be a second-generation AKM bayonet from the sixties, recognizable by the black steel pommel.