One of my professors asked this same question on day one of our jazz combo class. He asked everyone to write down their answers and pass them up to him.
He then read them aloud, and one by one, crumpled them up and tossed them away. Many were about the technical side, swing and syncopation etc., I'm pretty sure mine was one of those (this was almost 20 years ago so I don't remember my exact answer), all crumpled up and tossed casually over his shoulder. He got to one answer, chuckled, then put that one at the back of the stack, then resumed the reading, crumpling, and tossing of all of our freshman best guesses.
When he finally got back to that last page, he read it to us: "Jazz is weird." He left it at that and we pulled out our Real Books, but it stuck with me. Jazz is just weird, it doesn't need any other labels.