1. A protective system in automobiles in which when a crash occurs, a bag containing nitrogen, formed by the explosive decomposition of sodium azide, quickly inflates in front of the driver or passenger, preventing injury to the head. Side air bags, including the back seat passengers, also prevent injury.

2. A similar inflated bag used in performing stunts, etc.

3. (slang) A person who talks too much; a windbag or gossip.