Any short firearm with high firepower such as a shotgun, submachine gun, or "assualt" weapon. May have shortened stock or barrel, designed to be easy to maneuver in rooms and hallways. Called a "room broom" because you can quickly attack all adversaries in a room due to the small size and easy handling compared to a full sized battle rifle or shotgun.
A pistol would not qualify since it does not have the same firepower as a machine gun or shotgun
The special ops team was able to take out the entire room of terrorists from the doorway with their small but effective room brooms.