亡国 (wáng guó) literally means 'lost state'—'亡' (wáng) signifies 'to perish, to fall, to be destroyed', and '国' (guó) means 'state, nation, or country'. Together, the term refers to a nation that has been conquered, overthrown, or collapsed due to internal decay or external invasion. It carries strong historical and political connotations, often evoking images of dynastic collapse, foreign occupation, or national humiliation.

This word is primarily used in formal, historical, or literary contexts—not in everyday conversation. It frequently appears in discussions of Chinese history (e.g., the fall of the Ming Dynasty), classical texts, or modern political rhetoric warning against corruption or weakness. While grammatically a noun, it can function attributively (e.g., 亡国之君 'a ruler of a fallen state'). Its tone is solemn and often imbued with moral or cautionary weight.