What is Jazz?

Well most jazz in it's live context is improvised so I will say "Jazz is when a musician takes the internal sound his soul is creating and emits it externaly whether by instrument or voice"

The inverse of Classical music. Classical music, for the most part, celebrates the ensemble, symphony, quartet, playing together and in harmony. Jazz celebrates the individual playing around a theme each individual having the opportunity to express themselves while maintaining a unified whole, again in general. There are exceptions to both.

"If you have to ask what jazz is, you'll never know."- Louis Armstrong

"You blows who you is" - Louis Armstrong

"Hot can be cool & cool can be hot & each can be both. But hot or cool man, Jazz is Jazz." - Louis Armstrong

One of the many reasons Louis was the greatest jazz musician that ever lived.

I am not sure it can be defined in a definitive sense.
A musicologist would talk about the historical roots. Southern black music... spirituals, blues, gospel etc... And that would be very informative and very true. The great French Jazz violinist Stephane Grappelli once said, 'I never forget, it's a black art form'. He played it well, and made his contributions via his performances, but he never tried to define it or re-define it. This is the heart of the problem. Not so much, WHAT is Jazz, but, WHO should define Jazz. This problem exists in many genres of music.

The best answer for me is, to paraphrase the Supreme Court Justice's views about obscenity, I can't define Jazz, but I know it when I hear it. So we all live in different musical universes, and in my universe, the definition of Jazz is stored on that hard drive between my ears. Put there bit by bit during the years of my musical experiences.

One contributing factor in all this confusion concerning genre, is the idea, prevalent in this country, that a person can reach any goal, with hard work. This is a good positive idea in a general sense, but not absolutely true. When it comes to the arts, talent is the deciding factor. Talent trumps everything else. Desire and hard work are helpful, but talent is vital element. Some refuse to let a lack of talent stop them from reaching their goals.

The result is, we have guys from London calling themselves bluesmen. People from europe playing 'euro' Jazz. They make a lot of money and some of it sounds ok, but it ain't the real deal. Stephane never called his music 'euro Jazz'. hmmmmmm. I think the low point in my musical experience was listening to a German Country and Western band in Franfurt. I still cringe!!

Orpheus10: great question

What is not jazz? Classical, rock, country, techno, flamenco, Japanese traditional music etc. are not jazz. What remains could be called jazz. Perhaps any kind of music heavily based on improvisation can be called jazz. Is Indian music jazz too? Well, I wouldn't call it that but someone could call it Indian jazz. No objection from me. Persian music can be very impovisational too but not at all always so.
Yes, I don't like "classical jazz", with some exceptions.