Per wikipedia:
Hip hop music, also referred to as rap music, is a music genre typically consisting of a rhythmic vocal style called rap which is accompanied with backing beats. Hip hop music is part of hip hop culture, which began in the Bronx, in New York City in the 1970s, predominantly among African Americans and Latino Americans.[1][2] The term rap is often used synonymously with hip hop music.
Rapping, also referred to as MCing or emceeing, is a vocal style in which the performer speaks rhythmically and in rhyme, generally to a beat, recently, however, a difference has developed between "rapping" and "MCing". "MCing" has been used to describe those artists who possess and exercise superior lyrical ability and prowess. Beats are traditionally generated from portions of other songs by a DJ, or sampled from portions of other songs by a producer, though synthesizers, drum machines, and live bands are also used, especially in newer music. Rappers may perform poetry which they have written ahead of time, or improvise rhymes on the spot with or without a beat. Though rap is usually an integral component of hip hop music, DJs sometimes perform and record alone, and many instrumental acts are also defined as hip hop.
Hip hop arose in New York City when DJs began isolating the percussion break from funk, or rock songs for audiences to dance to. The role of the MC was originally to introduce the DJ and the music, and to keep the audience excited. The MC would speak between songs, giving exhortations to dance, greetings to audience members, jokes and anecdotes. Eventually, this practice became more stylized, and came to be known as rapping. By 1979, hip hop had become a commercially recorded music genre, and began to enter the American mainstream. It also began its spread across the world. In the 1990s, a form called gangsta rap became a major part of American music, causing significant controversy over lyrics which were perceived by some as promoting violence, promiscuity, drug use and misogyny. Nevertheless, hip hop continued to increase in popularity, and by the year 2000, it was a staple of popular music charts.