弹药 (dàn yào) literally combines 弹 (dàn), meaning 'bullet' or 'projectile', and 药 (yào), meaning 'medicine' or 'explosive compound'. Historically, 'medicine' referred to gunpowder—the explosive substance that propels projectiles—so the term evolved to mean 'ammunition': all consumable materials used in firearms and artillery, including bullets, shells, grenades, and rockets. It is a formal, collective noun and never used for individual rounds in everyday speech.

This word appears primarily in military, security, historical, or news contexts—not in casual conversation. It carries strong connotations of armed conflict, defense logistics, or law enforcement operations. Unlike English 'ammo', which can be informal, 弹药 is consistently formal and technical; it’s rarely pluralized or modified with measure words like 颗 or 发 in standard usage—it’s treated as an uncountable mass noun.