The Collaborative International Dictionary of English v.0.48:

Rap \Rap\, n.
   1. conversation; also, rapping.
      [PJC]

   2. (ca. 1985) a type of rhythmic talking, often with
      accompanying rhythm instruments; rap music.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

rap music \rap` mu"sic\ (r[a^]p` m[=u]"z[i^]k), n. (ca. 1985)
   a type of rhythmic talking, often with accompanying rhythm
   instruments; same as 7th rap, n..
   [PJC]

WordNet (r) 3.0 (2006):

rap music
    n 1: genre of African-American music of the 1980s and 1990s in
         which rhyming lyrics are chanted to a musical
         accompaniment; several forms of rap have emerged [syn:
         rap, rap music, hip-hop]