A restraining belt attached to a vehicle seat which is fastened around passengers and which is intended to keep a person in place in order to avoid injuries in accidents where the occupant could be thrown against a solid object.

A seat belt improves a passenger's chance of surviving a crash by 50 to 75 percent, mainly by preventing inertia from throwing the person through the windshield. It also spreads the force of an impact over a larger area of the body, making injuries less severe.

A seat belt also stretches which slows the passenger down with less velocity so the body feels less force.