What is Jazz?

As a self proclaimed expert and "aficionado", I should know the answer to that question; but I don't, because the answer is too complex.

As one example; Inna posted that he didn't like jazz, and in his next post he raved about a piece of music that I considered to be jazz. In Inna's case I understood the contradiction, he doesn't like "hard bop".

On the other hand, Rok2id's definition of jazz is so narrow that many of my jazz records and CD's, would be considered to be something other than "jazz".

What is "jazz" to you and can you define it?