The most strict definition of caliber is borrowed from Middle French "calibre", which means "internal diameter of a cylindrical object", such as a gun barrel's bore. Before the advent of the modern firearm cartridge a gun's projectile was a round ball, its diameter made to fit the barrel's bore, or it's caliber. Today's modern cartridges can have many shapes, sizes and powers regardless of the projectile's diameter or the gun barrel's bore. As such, a modern cartridge's caliber now defines its class, dimensions, power, and the type of gun that can use it. The example here shows various cartridges who's projectile diameters are roughly 0.22 inches, or ".22 caliber". But, their caliber descriptions must then include additional information to determine their actual class; i.e. .22 Short, .22 Long Rifle, .22 TCM, .22 Magnum, .22 Hornet, .218 Bee and .223 Remington.