What is a muscle car? Is it different from a sports car?

A muscle car is made for performance. The so called 'Muscle Car Era' started in the late 1960's with Detroit pumping out tonnes of horsepower in vehicles such as the Corvette, Camaro, Mustang, Nova, El Camino, Monte Carlo, Chevelle and many more.

The best muscle cars were back before the 80's when emissions laws were still being thought up or just introduced. This still allowed manufacturers to put the biggest engines in their cars that they could.

Some are still available today:

The Camaro (Sadly discontinued)
The Monte Carlo
The Mustang

In my opinion, Muscle cars are the best.

Fact from fiction, truth from diction. To add, a muscle car was usually a 2 door coup with big powerplants and a high top end. People increased the horsepower more by installing bigger cams and boring out the pistons to a larger diameter. Things you sadly cannot do anymore because of California's whimped out emmision laws.

The sports car is just that, for sport. A 2-seater with very limited cargo space. Lots of power, especially 0-60 quickness. It can be a convertible (ragtop), a convertible hard top (57 Corvette roadster and some Miadas}, or not ('73 Corvette Stingray). Most sports cars sadly were the product of Europe, Astin Martin, MGB, Triumph, Jaguar, Ferrari, Lamborgini, Maserati, BMW etc. The Corvette was the only sports car produced in the US that anyone really knows.

A muscle car is a car that comes with a high amount of horsepower. The size of the engine block has alot to do with it also. Most likely tehyre V8's, and put out alot of torque. Just like a Chevy 350 V8, like the one in my 69' Camero SS. Of course it really has 500hp but thats with a few modifications.

A muscle car is "typically" an intermediate sized car with a large engine installed ie, Chevelle SS396/454. This term originated with the GTO (Goat) of 1964 and continues to this day but meaning different things to different folkes. A 7-litre Galaxy could be considered a muscle car and therefore the term now seems to mean any car coming from the factory (and this is key...from the factory) with a high performance (ie muscle) engine. Modified cars have their own names like custom and rods etc.

The Mustang, Camaro, 'Cuda and such are refered to as "Pony" cars. This from the Mustang (get it? pony?) ( for those that don't know a real "Mustang" is a wild horse) which (in it's time) was a small, "compact" car with 2 doors and sporting pretensions.

A Sports car is a 2 seat convertible with racing pretensions although this definition became blurred in the '60's when GT cars became known as sports cars. GT cars being Grand Tourismo or Grand Touring cars typically with an enclosed passenger compartment and 2 seats (and probably 2 teeny, tiny rear seats).

This is only the beginning and you will find different opinions from different people depending on their age but I think you will find that these are the generally accepted "old school" terms and definitions.

In addition to the answers above, a muscle car can be a factory modified version of a sports car. A classic example is the Shelly Mustang. Ford starting building Mustangs, but sadly not enough people where buying them. So they called in a person called Carol Shelby. He took the mustang and turned into the icon it is today. Check out the link below.
http://www.quarterbore-inc.com/quarterbore-com/mustang/cl-shelby.htm

According to the dictionary, a muscle car is a high-performance automobile, often with flashy, sporty styling. A muscle car is usually an American made sedan. For example Camaro, Firebird, Roadrunner, Baracuda, Chevelle.

Owners sometimes modify their muscle car. For example, more powerful engine, noisy muffler, bigger tires, possibly racing accessories. See pictures here:

http://www.musclecars.net/topten.php