运气 (yùn qì) literally combines 运 (yùn), meaning 'to move' or 'to operate', and 气 (qì), meaning 'vital energy' or 'breath'. Together, they originally referred to the flow of cosmic energy influencing a person’s life circumstances — a concept deeply rooted in traditional Chinese philosophy. Over time, the term evolved into everyday usage to mean 'luck' or 'fortune', whether good or bad.

In modern Mandarin, 运气 is a neutral noun commonly used in casual and formal speech. It often appears with modifiers like 好 (good) or 不好 (bad), and can be discussed as something one 'has', 'gets', or 'runs out of'. Unlike English 'luck', it rarely functions as an adjective; instead, it's typically the subject or object of a sentence — e.g., '他的运气很好' (His luck is good). It’s frequently invoked when explaining unexpected outcomes, from passing an exam to finding a parking spot.