A fork of Rural Dictionary
originally (1964), a Ford Mustang (possibly after the Mustang logo), later to include competitors like the Chevrolet Camaro; by extension, a car whose main purpose is either to a) impress others, b) be fun to drive, c) run errands at high speed, or d) all of the above.
My grandfather has an old pony car in the garage. Keeps it in mint condition. Drives it on weekends.