Magic is probably one of the central elements of the Fantasy genre. However, magic in fiction seems to me much, much more complicated than what just calling it magic implies. This word is far too short for such a concept.
First of all, what I would call its mode of existence varies greatly from work to work. Magic may either be unnatural, supernatural, truly natural, etc. We’re not even talking about intrinsic goodness or evil here: magic in and of itself entails absolutely nothing metaphysically speaking. Its source will be anything one wants it to be, according to the narrative (and, possibly, the allegorical) needs of the author.