An all-terrain vehicle (ATV), also known as a light utility vehicle (LUV), a quad bike or quad, as defined by the American National Standards Institute (ANSI), is a vehicle that travels on low-pressure tires, has a seat that is straddled by the operator, and has handlebars. As the name implies, it is designed to handle a wider variety of terrain than most other vehicles. It is street-legal in some countries, but not in most states, territories and provinces of Australia, the United States, and Canada.

Street-legal, road-legal, or road-going, refers to a vehicle such as a car, motorcycle, or light truck that is equipped and licensed for use on public roads, being therefore roadworthy. This will require specific configurations of lighting, signal lights, and safety equipment. Some specialty vehicles that will not be operated on roads, therefore, do not need all the features of a street-legal vehicle; examples are a vehicle used only off-road that is trailered to its off-road operating area, and a racing car that is used only on closed race tracks and therefore does not need all the features of a street-legal vehicle. As well as motor vehicles, the street-legal distinction applies in some jurisdictions to track bicycles that lack street-legal brakes and lights. Street-legality rules can even affect racing helmets, which possess visual fields too narrow for use on an open road without the risk of missing a fast-moving vehicle.