'吹气' literally combines '吹' (to blow) and '气' (air or breath), meaning the physical act of expelling air from the lungs. It emphasizes directed, intentional airflow — not just breathing, but actively pushing air out through the mouth or nose. In everyday usage, it often refers to cooling something (e.g., hot soup), inflating objects (like balloons), or producing sound (e.g., on a flute). The action is typically conscious and effortful.

In clinical or technical contexts, '吹气' specifically denotes exhaling for diagnostic or therapeutic purposes — such as blowing into a breathalyzer, performing pulmonary function tests, or assisting resuscitation (e.g., mouth-to-mouth resuscitation). Unlike the general verb '呼吸' (to breathe), '吹气' never means inhalation; it always implies outward airflow. It’s neutral in register and commonly used in both spoken and written Chinese, especially in health, sports, and daily-life instructions.