Jazz
African American musical tradition since 1900.
What it means
Jazz designates a musical tradition that arose around 1900 in the United States from African American roots and has since branched into numerous style directions. Common features are the central role of improvisation, a special rhythmic shaping with displacements against the basic pulse, a personally shaped tone on the respective instrument, and music-making over harmonic models that serve as a basis instead of fixing every note.
Musical use
Many pieces rest on a theme with subsequent improvisation over its chord progression; recurring models such as the twelve-bar blues form the frame for this. The rhythm section of bass, drums, and chord instrument supplies pulse and harmony over which winds or other soloists play. Notation is often limited to melody and chord symbols; the work exists not as a score but in performance and in recordings. The development ran through many styles whose boundaries are fluid, and influenced the music of the twentieth century far beyond its own field.
Performance practice
Learn through listening: recordings are the authoritative source here, not the score. Practise scales and chord arpeggios over chord progressions, but aim at melodic lines instead of exercise patterns. Work on the rhythmic groundwork before you turn to complex harmony; without it everything else sounds uninvolved. In ensemble playing, listen to the rhythm section and adapt instead of imposing your own ideas of time. Practise accompanying as seriously as soloing.
Bear in mind that notation in jazz supplies only a framework: melody and chord symbols say nothing about phrasing, tone colour, and handling of time, which make up the style. This side is learned by listening and by playing along with recordings. Transcribe solos by ear, because phrasing and timing appear in the notation only incompletely. Know the form of a piece by heart and count it along. In the ensemble, settle key, form, and number of choruses before you begin.
While listening, note down the form and the chord progression instead of merely playing along melodies.