Rock n Roll (often written as Rock & Roll, Rock 'n' Roll, or Rock and Roll) is a genre of popular music that evolved in the United States during the late 1940s and early 1950s. It originated from black American music such as Gospel, Jump Blues, Jazz, Boogie Woogie, Rhythm and Blues, as well as Country music.
While Rock n Roll's formative elements can be heard in Blues records from the 1920s and in Country records of the 1930s, the genre did not acquire its name until 1954. According to journalist Greg Kot, "Rock and Roll" refers to a style of popular music originating in the United States in the 1950s. By the mid-1960s, rock and roll had developed into "the more encompassing international style known as rock music, though the latter also continued to be known in many circles as rock and roll."
In the earliest Rock n Roll styles, either the piano or saxophone was typically the lead instrument. These instruments were generally replaced or supplemented by guitar in the middle to late 1950s. The beat is essentially a dance rhythm with an accentuated backbeat, almost always provided by a snare drum. Classic Rock n Roll is usually played with one or two electric guitars (one lead, one rhythm) and a double bass (string bass). After the mid-1950s, electric bass guitars and drum kits became popular in classic rock.
Rock n Roll had a polarizing influence on lifestyles, fashion, attitudes, and language. It is often depicted in movies, fan magazines, and on television. Rock n Roll may have contributed to the civil rights movement because both Black American and White American teenagers enjoyed the music.

See the full article on Wikipedia
Listen to some old and new examples of Rock n Roll Jivers below.