军火库 literally combines three characters: 军 (jūn, 'military'), 火 (huǒ, 'fire'—here used in the historical sense of 'firearms' or 'gunpowder weapons'), and 库 (kù, 'storehouse' or 'depot'). Together, it means a secure facility where weapons, ammunition, explosives, and other military equipment are stored, maintained, and distributed. It is a formal, official term often used in news reports, military contexts, and geopolitical discussions.

The word carries strong connotations of strategic importance, security risk, and state control. While it can refer to real physical installations, it’s also used metaphorically—for example, to describe a country with vast arms manufacturing capacity or a region heavily saturated with weapons. Unlike general terms like 仓库 (cāngkù, 'warehouse'), 军火库 specifically implies military-grade armaments and strict regulation.