A car is a wheeled, self-propelled vehicle. Normally, a car has 4 wheels and is designed for the transport of passengers. Depending upon locale, cars may also be called 'autos.'
Another distinctive feature of the car, at least within the US, is that a car generally builds a cockpit-type frame that protects the driver (also cage). Contrast that with the "cage-less" design of three-wheeled motorcycles such as the Can-Am Spyder.