Well, aluminum cases means that the cases themselves are aluminum, rather than the usual brass. Unlike brass, aluminum cases are generally not reloadable.
Boxer refers to a type of primer. There are basically two types, the other is called Berdan. Generally, Boxer primers are easily reloadable, while Berdan require a special tool, and are considered not worth the effort.
Large pistol refers to the size of primer. There are a few different kinds/sizes of primers depending on what type of ammo you're reloading.