When I was in high school, I had to take a class called "Theory of Knowledge". It was all about how people think, why they think the way they do, how culture affects thinking, systems of thinking and philosophy, etc. Basically, it was a class in which all we did was think about thinking. Which was way more interesting in practice than it sounds.

ANYWAY, one of the classes was on the definition of art. We each had to draw a picture at the beginning of class. So we're drawing away, making all sorts of crazy pictures with magic markers that would make the masters cry in agony. Then, together as a class, we came up with a definition of art. I don't remember our exact definition, but I do remember that the guy that drew a black outline of the clock above the chalkboard created the only piece of art by our definition.

Moral of the story- I have no definition of art, except as an expression of one's inner emotions.