A custom car is a passenger vehicle that has been altered to either improve its performance, change its aesthetics, or a combination of both. Some automotive enthusiasts in the United States want to push "styling and performance a step beyond the showroom floor - to truly craft an automobile of one's own." A custom car in British according to Collins English Dictionary is built to the buyer's own specifications.

Hot rods are typically American cars that might be old, classic, or modern and that have been rebuilt or modified with large engines optimized for speed and acceleration. One definition is: "a car that's been stripped down, souped up and made to go much faster." However, there is no definition of the term that is universally accepted and the term is attached to a wide range of vehicles. Most often they are individually designed and constructed using components from many makes of old or new cars, and are most prevalent in the United States and Canada. Many are intended for exhibition rather than for racing or everyday driving.