Ponies

Pony is the species of the main characters of the show, and its namesake. So far three types of ponies have been named:
 * Earth ponies
 * Pegasus ponies
 * Unicorn Ponies

The princess characters are named unicorns but have wings like the Pegasus kind too.

As there have not been any humans or any measurements stated in the series, their comparative size to us is unknown. Wikipedia caps the size of ponies with this statement:
 * "In modern use, many organizations define a pony as a mature horse that measures less than 14.2 hands (58 inches, 147 cm) at the withers, but there are a number of exceptions. Different organizations that use a strict measurement model vary from 14 hands (56 inches, 142 cm) to nearly 14.3 hands (59 inches, 150 cm)."

The ponies in the show do not refer to themselves as horses, but some such as Trixie have referred to themselves as "equine".

Much of ponies' speech patterns reflect the substitution of their physical attributes in place of human ones we are accustomed to using, such as saying "hooves" in place of hands, or "mane" in place of hair. This is demonstrated in catch phrases such as "it's out of my -" or "get out of my -".