Jazz is an original American art form that began in the southern United States in the early 20th century.
Three basic elements set this art form apart from classical music:
While most classical and jazz music looks the same, the rhythms are performed differently. Classical music typically places an emphasis on the first and third beats of each measure. Jazz music switches that emphasis to beats two and four, as well as placing an emphasis on the upbeats. The tension created by switching the emphasis to the second and fourth beats and the stressing of upbeats within the measure is called syncopation.
One of the basic differences between jazz and classical music is that jazz musicians improvise. Musical improvisation is a creative process that requires the jazz artist to be spontaneous, composing music with on their instrument or scat singing music that has never been played or written down before.
Classical music is composed before the concert begins. Jazz musicians play a composed tune to start and follow with improvisation that is composed on the spot. Jazz is never the same. It changes each time because the musical "conversations" that occur change as jazz musicians perform. An improvised idea from a trumpet player might be responded to by the supporting piano player, and then responded to again by the trumpet player.
Using words to describe the improvisation, the conversation between the two musicians might seem like this:
Trumpet player: That pizza was delicious.
Piano player: Yeah man, delicious.
Trumpet player: Delicious and hot.
What is Jazz? Video Lesson
This video from the National Museum of American History explains that jazz is improvisation, collaboration, and a conversation with the players in the band. It features images of jazz greats and current musicians.