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An airbag is part of a vehicle's safety restraint system, a flexible envelope designed for rapid inflation in an automobile collision, to prevent vehicle occupants from striking hard interior objects such as steering wheels. It is considered a "passive" safety component not requiring any input or action from the user, rather than an "active" component — such as a seat belt, which requires fastening.

Various manufacturers have over time used different terms for airbags. General Motors' first bags, in the 1970s, were marketed as the Air Cushion Restraint System. Common terms in North America include Supplemental Restraint System (SRS) and Supplemental Inflatable Restraint (SIR); these terms reflect the airbag system's nominal role as a supplement to active restraints (i.e., seat belts).

The efficacy of airbags in saving lives and preventing injuries is a controversial subject. One study, cited below, puts the number at just under 400 per year (6,000 total), and another study indicates that airbags reduce fatalities by 8% when seat belts are worn.