Jazz rap

Jazz rap is a fusion of hip hop and jazz, developed in the late 1980s and early 1990s. The lyrics are often based on political consciousness, Afrocentricity, and general positivism. Allmusic writes that the genre "was an attempt to fuse African-American music of the past with a newly dominant form of the present, paying tribute to and reinvigorating the former while expanding the horizons of the latter". Musically, the rhythms have been typically those of hip hop rather than jazz, over which are placed repetitive phrases of jazz instrumentation: trumpet, double bass, etc. The amount of improvisation varies between artists: some groups improvise lyrics and solos, while a great deal of them do not.

Source : http://en.wikipedia.org/wiki/Jazz_rap