A cartridge is a small container that holds materials needed for a specific purpose. In the world of printing, a cartridge typically contains ink or toner, which is used by printers like the HP LaserJet or Canon PIXMA to create text and images on paper. When the cartridge runs out, it can be replaced to continue printing. In the context of firearms, a cartridge refers to a complete unit of ammunition. It includes a bullet, gunpowder, and a casing. When fired, the gunpowder ignites, propelling the bullet out of the barrel of a rifle or handgun. Each type of firearm uses specific cartridges designed for its caliber.