Glad you asked, EX.
NASCAR is the National Association of Stock Car Automobile Racing. They race in many different divisions, but always stock cars. (Well, there is a division for stock trucks.) Their top division is the Cup cars that features such stars as Jeff Gordon, Dale Jarrett, Mark Martin, Sterling Marlin, Jeff and Ward Burton and Bobby and Terry LaBonte. NASCAR has been the top governing body of of stock car racing for over 50 years. Although they race on the same tracks as other types of cars(such as Indy Cars), they only race stock cars.
What's a stock car? Well, it sure isn't stock!
Back in '49 they were pretty much showroom cars with very few alterations allowed, but over the years they have changed greatly and now only look like stock cars. In their defense, most of the changes have been in the interest of safety.
I saw my first NASCAR race at the Nashville Fairgrounds in 1952. The track then was a one-mile dirt oval and the race included Fords, Chryslers, Oldsmobiles, Hudsons and even a Nash.
I was hooked for life.
I hope you're not sorry you asked.
Howard