Barrel shroud

A barrel shroud is an external covering that envelops (either partially or full-length) the barrel of a firearm, to prevent unwanted direct contact with the barrel (e.g. accidental collision with surrounding objects, or the user accidentally touching a hot barrel, which can lead to burns). Moving coverings such as pistol slides, fore-end extension of the gunstock/chassis that do not fully encircle the barrel, and the receiver (or frame) of a firearm itself are generally not described as barrel shrouds, though they can functionally act as such.
A handguard is a type of (often only half-length) barrel shrouding that is designed specifically for the user to grip the front of the gun for better stability and control.
Full-length barrel shrouds are commonly featured on air-cooled machine guns, where frequent rapid bursts or sustained automatic fire will leave the barrel extremely hot and dangerous to the user. However, shrouds can also be utilized on semi-automatic firearms, especially the ones with light-weight barrels, as even a small number of shots can heat up a barrel enough to injure the user in certain circumstances.
Barrel shrouds are also used on pump-action shotguns. The military trench shotgun features a ventilated metal handguard with a bayonet attachment lug. Ventilated handguards or heat shields (usually without bayonet lugs) are also used on police riot shotguns and shotguns marketed for civilian self-defense. The heat shield also serves as an attachment base for accessories such as sights or sling swivels.