Jazz, a form of instrumental and vocal music characterized by syncopated rhythms and informal improvisation, has been called America's only original art form. If you've ever listened to Louis Armstrong, Miles Davis, John Coltrane, or Thelonious Monk, jazz is what you're hearing.
The term jazz originated not with music, but in baseball, where it was used as a synonym for "pep, vim, vigor." It began to be used to describe music about a decade after jazz first began to be played in 1900 New Orleans. Since then, like the art form it describes, jazz has changed and expanded its meaning. Today, jazz can refer to a genre of dance, to the act of "sprucing something up," to the decade of the 1920s (nicknamed The Jazz Age), or to holding your hands above your head and waving your fingers, making jazz hands.