A mage is any human that can cast spells.
It is believed that mages were originally humans that envied dragons. They practiced fighting, but were never strong enough. One day, a dragon that was betrayed by his own kind gave the humans all of his powers until he died powerlessly. The humans became powerful and called themselves mages. Although, since the power came from a dragon, it doesn't affect dragons.
List of Alive Mages
List of Late Mages
There are none so far mentioned in any stories.