The definition of muscle car is subjective and frequently debated. Muscle cars often have many of the following characteristics:
- A large V8 engine in the most powerful configuration offered for a particular model
- Rear-wheel drive
- Being manufactured in the United States in the 1960s or early 1970s (the specific year range of 1964–1973 is sometimes used)
- A relatively lightweight two-door body (opinions vary as to whether high-performance full-size cars, compacts, and pony cars qualify as muscle cars, as it is sometimes claimed that only intermediate cars can be considered muscle cars)
- An affordable price
- Being designed for straight-line drag racing, while remaining street legal.
High-power pony cars are sometimes considered muscle cars, however personal luxury cars and grand tourer cars are often too expensive to be considered muscle cars. Sports cars and sports sedans are not usually considered muscle cars, since they are generally associated with circuit racing rather than drag racing. Muscle cars are an extension of the hot rodding philosophy of taking a small car and putting a large-displacement engine in it, for the purpose of increased straight-line speed.
This section may be unbalanced towards certain viewpoints
. (February 2019)
Muscle cars were originally referred to as "Supercars" in the United States, often (though not always) spelled with a capital S." From the mid-1960s to the mid-1970s, "dragstrip bred" mid-size cars were equipped with large, powerful V8 engines and rear-wheel drive were referred to as Supercars more often than muscle cars. An early example is the 1957 Rambler Rebel, which was described as a "potent mill turned the lightweight Rambler into a veritable supercar."
In 1966, the supercar became an official industry trend" as the four domestic automakers "needed to cash in on the supercar market" with eye-catching, heart-stopping cars. Examples of the use of the supercar description for the early muscle models include the May 1965 Car Life road test of the Pontiac GTO along with how "Hurst puts American Motors into the Supercar club with the 390 Rogue" (the SC/Rambler) to fight in "the Supercar street racer gang" market segment, with the initials "SC" signifying SuperCar.
The supercar market segment in the U.S. at the time included special versions of regular production models that were positioned in several sizes and market segments (such as the "economy supercar"), as well as limited edition, documented dealer-converted vehicles. However, the supercar term by that time "had been diluted and branded with a meaning that did not respect the unique qualities of the 'muscle car'."