Many of the older guys may remember when the magazines debated car name classifications for a couple years, in the late sixties. As I recall it all came down to this:

When modified for more power....

'48 and older were "street rods". (There was also a big styling change going into '49.)

Post World War Two cars were street machines.

'64 -'72 Detroit big block "performance cars" were "Muscle Cars".

...and later, the cars that would be "street machines" became "Pro Street" if they had giant tires.