Well, I'm trying, as much as I can, to find specific and coherent ways to define and explain magic.

I studied sciences, so I especially like the statement of Arthur C. Clarke "Any sufficiently advanced technology is indistinguishable from magic."
In my Elzevir universe, I explain magic by the possibity to act through an other dimension, a kind of parallel universe. The "magicians" are in fact using tools of this other dimension, and have the talent, at some point, to mingle the two for an instant. So, the magician is using a weapon from his point of view, but for the normal people, he is just moving his hand toward is target (if you follow me).

In an other of my rpg, I'm using the "eggregor" esoteric/philosophy concept (the name of the game by the way) which states that the more people believe in something, the more real it becomes.

Anyhow, an interesting and fundamental basis for a lot of "imaginary" and fantastic worlds !