Friend and author Taylor Ellwood is featured in the Semantikon e-zine. In addition to some writing, there’s an interview with him where he gives the best definition of magic I’ve seen:
Magic, as I spell it, is making the improbable possible. In other words it’s learning how even the slightest change you make can have a radical effect on the internal system of your psychology, and the external system of the environment and universe we live in. Magic is the realization of an interdependent system of life that needs every part to bring forth the hidden potential.