Under the so-called barrel, one understands the part of a firearm through which the projectile (also known as a bullet) is guided during firing. The projectile "passes through" the barrel of the weapon. Therefore, it is referred to as the barrel. 

Especially in relation to hunting weapons, a distinction is made between the rifle barrel and the shotgun barrel, as these have significantly different characteristics and are also designed for different types of ammunition.

Other terms relevant to barrels include special forms of barrels such as insert barrel, exchange barrel, interchangeable barrel, double barrel, and triple barrel.