An armory or armoury is a place where arms and ammunition are made, maintained and repaired, stored, issued to authorized users, or any combination of those. Over the centuries, this has included every variant of such a place, whether privately or publicly owned (with the latter in older royal and modern state-owned versions).
Armories and arsenals are both places where arms or ammunition may be made, maintained and repaired, stored, or issued. The usage differences between the names is mainly a matter of historical linguistic development. It is a common principle in natural language that synonyms have subtle connotative boundaries (albeit ones that may be somewhat permeable over time and distance).
Today an armory is typically a military depot used for the storage of weapons and ammunition. The term may also apply to an area within a building used for the storage of weapons. In a typical armory, ammunition is stored separately from weapons (both under lock and key) to minimize the potential for misuse, theft, and safety breaches. Very sensitive alarm systems are also extensively used.