A stock car in the original sense of the word is an automobile that has not been modified from its original factory configuration. This term was used to differentiate such a car from a race car, a special, custom-built car designed only for racing purposes with no intent of its ever being used as regular transportation.

When NASCAR was first formed by William France Sr. to regulate stock car racing, there was a requirement that any car entered be made entirely of parts available to the general public through automobile dealers, and that all cars must be from a model run of which at least 500 cars of that model were sold to the general public.

In NASCAR's early years, the cars were so "stock" that it was commonplace for the drivers to drive themselves to the competitions in the car that they were going to run in the race.

Stock car racing is a form of automobile racing found mainly in the United States and Great Britain held largely on oval rings of between approximately Ѕ mile and 2.66 miles (about 0.8 to 4.2 kilometres) in length, but also raced occasionally on conventional racing circuits, also known as road courses.

Ovals shorter than one mile (1.6 km) are called short tracks; unpaved short tracks are called dirt tracks; longer ovals are typically known as superspeedways. Races are generally 200 to 600 miles (300-1000 km) in length.

Average speeds in the top classes are around 160 mph (275.5 km/h), compared to 220 mph (354 km/h) in comparable levels of open wheel racing. Some NASCAR races can get up to speeds of 200 mph at tracks such as the Daytona International Speedway and the Talladega Superspeedway.