Jazz is an expression of thought and feeling. It can be slow and melancholy, or quick and light. It's simply what the musicians feel at the time. It's mainly instrumental, but sometimes there can be singing. I've read some of the definitions, apparently some dislike the lack of word. Well some things can't be expressed in words.
Would be a great and usefull place, if it weren't for the thousands of pointless definitions. Much of these are just people trying to make up their own word, named after themselves. If you search hard, you may be able to find a usefull bit. Though this is possibly the best place to go if you want to learn a sex position, they are not in short supply.