* Relatively small size and price: They were smaller and more affordable than full-sized cars, but larger than compact cars.
* Sporty styling and performance: They offered a sporty image and generally had more powerful engines than their more practical counterparts.
* Youth-oriented marketing: They were targeted towards younger buyers, emphasizing style and excitement.
The "pony" part of the name is thought to have come from a combination of factors, though there's no definitive single answer. It likely evoked a sense of small, spirited, and powerful animals—characteristics that fit the car's image. Some suggest the name was inspired by the powerful Mustang horse itself.
In short, the Mustang wasn't *called* a pony car initially, but its features and marketing helped create and solidify the "pony car" category as a genre of American automobiles.