What is jazz? It's a classic American dance style, that over the years has evolved greatly and consequently become difficult to define. It changes over time, interacting with the other styles it meets along the way, resulting in fusions like Latin jazz, street jazz and Afro-jazz etc
Classical Jazz is a style performed from the core, with clean and strong lines and contractions emanating from the hips and chest. It uses isolations, parallel passes, shoulder twists and hinges. The style of dance was heavily influenced in the early days by Jack Cole, Gus Giordano, Matt Mattox and Luigi.
Contemporary Jazz challenges the rules and foundations of classical jazz. It adds in more pedestrian movements and introduces story lines and self expression. Choreographers might use unconventional body parts (elbow, rib, etc) or shifts of weight to break the conventional line.
In more recent times, Commercial Jazz has taken the forefront in the genre. It is a mix of more classical jazz steps with hip hop and the latest dance steps of the day. Created in response to the surge of pop video productions in the early 80's and the need for back-up dancers in these videos. Emphasis is on impressive tricks such as leaps, flips and turns. Movements are often very literal to the lyric of the song and choreographic themes are lheavily lead by changes in the music.