Hip-hop is a genre of popular music that emerged in the early 1970s alongside an associated subculture created by African-American and Afro-Caribbean communities in New York City. The musical style is a synthesis of a wide range of techniques, but rapping is frequent enough that it has become a defining characteristic. Other key markers of the genre are the disc jockey (DJ), turntablism, scratching, beatboxing, and instrumental tracks. Cultural interchange has always been central to the hip-hop genre: It simultaneously borrows from its social environment while commenting on it.