‘哈气’ is a verb meaning to exhale warm, moist breath onto a cool surface—most commonly to fog up glass, a mirror, or a window. The first character 哈 (hā) imitates the sound and action of forcefully exhaling, while 气 (qì) means 'air' or 'breath'; together, they literally mean 'to blow out breath.' This action is often used intentionally for practical purposes, like cleaning lenses (by fogging then wiping), checking if a surface is cold, or creating temporary condensation for drawing or testing temperature.

The word is informal but neutral in register and frequently appears in everyday spoken and written Chinese. It’s not used for general breathing (that’s 呼吸), nor for blowing air from the mouth without moisture or warmth (e.g., blowing out a candle is 吹灭). It specifically implies warm, visible exhalation—especially in cool environments—and often carries a slight physical or sensory nuance, such as warmth, fog, or condensation.