What is Art?

The age old question and really I'm getting tired of it personally. No one seems to agree and makes the same arguement that has been going on for ages. Recently I had my "art" teacher tell me illustration was not art and that abstraction is a purer form of art. Frankly I was insulted that she completely dismissed a whole sector of people doing what I would consider some amazing works of art. I'm still trying to get my head around what she thinks gives her the devine insight to define art for others. As far as my concern I think art is better undefined if nothing gets done but demeaning others and passing them over because they don't cater to the abstract or realist tastes. Anyway I shall rant again later