Before there was hip hop, there was toasting--invented by URoy and jamiacan sound system artists, its the act of rapping poetry over a song as it's playing, as a DJ might do to "Toast" an artist.  This was the song that convinced radio executives that the US public endorsed such rapping, breaking the airwaves open for bands like Grandmaster Flash, who had struggled for airtime. A few months from this, release, RUN DMC dropped their first album and the rest was history.