I can tell the age of posters on this thread by replies.
In the 1960's and 1970's GM used a letter based classification to designate body style/structure/size across its brands of Chevrolet, Pontiac, Oldsmobile, and Buick. Within these classifications their was various engine choices and performance trim packages...mainly due to the performance engines being offered at the time.
The GM "A-Body" was the Chevy Chevelle, Pontiac GTO/LeMans, Olds Cutlass, and Buick Skylark/GS.
They were marketed to compete against the Ford Torino and Plymouth and Dodge "B-body" (Plymouth and Dodge body designations were different than GM) being the Road Runner and variants, and the Dodge Charger and variants.
Depending on performance engine choices and performance trim packages would designate them as considered "muscle cars".
The GM "B-Body" was the Chevrolet Impala, Pontiac Catalina/Bonneville, Olds Delta 88, and Buick Wildcat or Lesabre. These were marketed to compete against Plymouth Fury, Dodge Coronet variants and Ford Thunderbird and Galaxy.
Again, performance high HP engine options and performance trim packages could put the above in a "muscle car" category.
The GM "F-Body" was the Pontiac Firebird/Trans Am and Chevrolet Camaro. Designated as "pony cars" they were marketed against the Ford Mustang and variants and the Plymouth Barracuda and Dodge Challenger.
Again, certain performance engine options and performance trim packages would put them in the muscle car category.
The GM "X-Body" was the Chevrolet Nova, Pontiac Ventura, Olds Omega. They were to compete against the Dodge Demon and Plymouth Duster as "compact cars". Same as above, some models offered high performance engine and trim packages that would put them in the muscle car category.
Regardless, John DeLorean of then General Motors, is credited of being the father of the muscle car era with the introduction of the 1964 GTO variant of the then LeMans of Pontiac.
TAMU Wildlife and Fisheries Sciences
Boat racing is like a beautiful woman.......expensive, high maintenance, but well worth the fun!