Wordnet 3.0
NOUN (1)
1. 
 a genre (usually a cappella) of Black vocal-harmony music of the 1950s that evolved in New York City from gospel singing; 
 characterized by close four-part harmonies; 
 the name derived from some of the nonsense syllables sung by the backup; 
WordNet (r) 3.0 (2006):
doo-wop
    n 1: a genre (usually a cappella) of Black vocal-harmony music
         of the 1950s that evolved in New York City from gospel
         singing; characterized by close four-part harmonies; the
         name derived from some of the nonsense syllables sung by
         the backup