NOUN: 1. An automobile of a standard make modified for racing. 2. A railroad car for carrying livestock."http://www.bartleby.com/61/75/S0767500.html
an ordinary car that has been made stronger and faster so that it can be driven in special races"http://www.freesearch.co.uk/dictionary/stock+car
"A stock car in the original sense of the word is an automobile which has not been modified from its original factory configuration. This term was used to differentiate such a car from a race car, a special, custom-built car designed only for racing purposes with no intent of its ever being used as regular transportation.
This was eventually modified, however, primarily in the interest of safety, as race drivers are subjected to forces unheard of by drivers of cars in ordinary use, and require a far higher level of protection than is normally afforded by truly "stock" automobile bodies. Modern racing "stock" cars are stock in name only, using a body template modeled after currently-available automobiles, but the chassis, running gear, and equipment have almost nothing to do with those of ordinary automobiles."http://www.reference.com/browse/wiki/Stock_ca...