In Greek myth, a pterippus was the name for any winged horse with the ability to fly. The plural is 'pterippi'. They are all descended from Pegasus and Euippe. Pegasus was a winged horse that sprung forth fully-formed from Medusa's blood when Perseus decapitated Medusa. He married Euippe (or, some say, her sister Ocyrrhoe), who was the daughter of the centaur Cheiron, and they had two children, Celeris and Melanippe. Exactly how the rest of the pterippi were produced, history does not relate; however it can be assumed that having wings proved to be a dominant trait, while having a human torso did not.
These days a winged horse is more likely to be called a pegasus (plural, pegasi). This is technically incorrect; Pegasus could be considered a pterippi himself, but he was only one individual.
Related beasts include the hippolepididopterus or papillequine, pterocentaur, pyrippus, and hippogriff. Other winged horses are Alborak (AKA Boraq or Burak), Alsvidur, Arvakur, and Mamoun.