Pegasus are a race of magical winged horse that is well-known in myths and fables that they are featured in one of Chariot cards.
Pegasus is basically a magical creature which physiology greatly similar with that of horse, but has a pair of large bird-like wings on its shoulders which strong enough to provide prolonged flight. One that featured in Chariot card has brown/golden hair and feathers, though the tail hair of the creature Akko acquired in Sub Event Build A Shooting Star! has silverish color, suggesting there are at least two known species of the creature.
Pegasus' tail feather is one of materials used to construct a Shooting Star.