Essence of Jazz
The core of jazz is improvisation. This is also what sets apart jazz music from many other forms of music. A friend of mine, who is a keen composer, once asked me, " don't you jazz musicians get bored of playing the same standards all the time over and over again" and I replied "Well, the thing is, everytime we play it is different from the last, and we seldom know what's going to happen next."
Check out this video of some great musicians jamming away at casino lights '99 montreaux ...