Jazz originated in African American communities in the 1800s and onward and as generations passed it also evolved in styles. Ragtime and jazz rock fusion are also important contributors to the style it is today. By nature, jazz is improvisational and uses more complex compositional techniques like polyrhythms. Because the genre spread so far around the world it drew upon many artistic styles and international cultures. And so today you might see variations like New Orleans, Kansas City, Bebop or even Gypsy. The 1940s was a turning point in the genre, as it welcomed more songs that were softer and linear. One decade later however and the trend went back to free and experimental. One thing you can say about jazz is that it steadily evolves as culture intermingles.
Jazz incidental music when used in the background of a film or radio show, obviously has to fit the subject matter because it could be distracting if used for an esoteric purpose. When you think of jazz used in TV or movies as background noise, you usually think soft and warm pieces designed to help viewers feel comfortable in the setting. The instruments chosen might include trumpets, drums and saxophones. Sometimes big band instruments are used to create a unique sound. Tempos of good jazz could be anything from mellow and laid back to mid tempo or lively.
Royalty free jazz music could help your production, whether you want to establish atmosphere, cast a mood over a scene or the introduction of a documentary, or even make a film about music itself with famous tunes in the soundtrack. The good news is that you can download them all via mp3 or wav. Because of the loose and freeform nature of the genre timing may be less strict when it comes to splicing sound with visuals.