Rock music is a genre of popular music that originated as "rock and roll" in 1950s America and developed into a range of different styles in the 1960s and later, particularly in the United Kingdom and the United States.It has its roots in 1940s' and 1950s' rock and roll, itself heavily influenced by rhythm and blues and country music. Rock music also drew strongly on a number of other genres such as blues and folk, and incorporated influences from jazz, classical and other musical sources.
The sound of rock is traditionally centered around the electric guitar, which emerged in its modern form in the 1950s with the popularization of rock and roll. The sound of an electric guitar in rock music is typically supported by an electric bass guitar pioneered in jazz music in the same era, and percussion produced from a drum kit that combines drums and cymbals. This trio of instruments has often been complemented by the inclusion of others, particularly keyboards such as the piano, Hammond organ and synthesizers.A group of musicians performing rock music is termed a rock band or rock group and typically consists of between two and five members. Classically, a rock band takes the form of a quartet whose members cover one or more roles, including vocalist, lead guitarist, rhythm guitarist, bass guitarist, drummer and occasionally that of keyboard player or other instrumentalist.
Since its early development rock music has been associated with rebellion against social and political norms, most obviously in early rock and roll's rejection of an adult-dominated culture, the counter-culture's rejection of consumerism and conformity and punk's rejection of all forms of social convention, however, it can also be seen as providing a means of commercial exploitation of such ideas and of diverting youth away from political action.

Rock Music Encyclopedia
The foundations of rock music are in rock and roll, which originated in the United States during the late 1940s and early 1950s, and quickly spread to much of the rest of the world. Its immediate origins lay in a melding of various black musical genres of the time, including rhythm and blues and gospel music, with country and western. In 1951, Cleveland, Ohio disc jockey Alan Freed began playing rhythm and blues music for a multi-racial audience, and is credited with first using the phrase "rock and roll" to describe the music.

Elvis Presley in a promotion shot for Jailhouse Rock in 1957 Debate surrounds which record should be considered the first rock and roll record. Contenders include Goree Carter's "Rock Awhile" (1949); Jimmy Preston's "Rock the Joint" (1949), which was later covered by Bill Haley & His Comets in 1952 and "Rocket 88" by Jackie Brenston and his Delta Cats (in fact, Ike Turner and his band The Kings of Rhythm), recorded by Sam Phillips for Sun Records in 1951. Four years later, Bill Haley's "Rock Around the Clock" (1955) became the first rock and roll song to top Billboard magazine's main sales and airplay charts, and opened the door worldwide for this new wave of popular culture



Rock music is traditionally built on a foundation of simple unsyncopated rhythms in a 4/4 meter, with a repetitive snare drum back beat on beats two and four. Melodies are often derived from older musical modes, including the Dorian and Mixolydian, as well as major and minor modes. Harmonies range from the common  to parallel fourth and fifths and dissonant harmonic progressions. Rock songs from the mid-1960s onwards often used the verse-chorus structure derived from blues and folk music, but there has been considerable variation from this model. Critics have stressed the eclecticism and stylistic diversity of rock.

Because of its complex history and tendency to borrow from other musical and cultural forms, it has been argued that "it is impossible to bind rock music to a rigidly delineated musical definition.

list of rock sub-genres