The so-called barrel is the part of a firearm through which the bullet (also projectile) is guided when the shot is fired. The projectile "passes through" the barrel of the firearm. Therefore, this is referred to as the barrel.

Especially with regard to hunting weapons, a distinction is made between the rifle bar rel and the shotgun barrel, as these have substantially different characteristics and are also designed for different types of ammunition.

Other relevant terms in relation to barrels are those of the barrel special forms such astuck-in barrel, exchange barrel, exchange barrel, double barrel as well as tripe barrel.