What is a "short" in this context?

In the 1974 movie Phantom of the Paradise, there is a line in the song “Upholstery,” which is about cars, and which says,

“Of all life’s mysteries the greatest one I’ve seen:
My short runs better when it’s clean.”

What is a “short” in this context?

U.S. slang for a car.

♫ ♬ It happened on the strip where the road is wide /
Two cool shorts standing side-by-side…

From the Oxford English Dictionary: