Rhythm and blues (R&B) is a style of music that grew out of 1940s black American music styles including blues and jazz. The style, chord structure and rhythms of rhythm and blues music deeply influenced both black and white American pop music during the 20th century. This term's meaning expanded in the late 20th century to include any predominantly black form of music.
As its name suggests, one of the major influences on rhythm and blues music was the blues. The blues is a style of music based off of a very specific 12-measure chord progression: four measures of the I chord, two of the IV chord, two of the I chord, one of the V or V7 chord, one of the IV chord, and two of the I chord. Rhythm and blues music adopted this progression in the 1940s and 1950s, sometimes tweaking it along the way, and made it more a part of mainstream American pop music.
Other influences on rhythm and blues include jazz, swing and boogie. Early R&B music usually featured a solo vocalist with a brass-heavy orchestra accompaniment. It usually had strong, often syncopated rhythms well-suited to the dance hall.
Especially during the 1950s, there was a give-and-take relationship between rhythm and blues and rock and roll. Although the first was predominant in black culture and the second in white culture, the two often borrowed from one another. Elvis Presley, for instance, recorded a number of songs that feature blues-influenced structures and vocal styles. One of the most famous of these was "Hound Dog."
Leading up to the civil rights movement of the 1960s, many black artists used their music as a platform to speak out against segregation and racial inequalities. Big Bill Broonzy's "When Will I Get To Be Called A Man" describes the life of a black man who is constantly referred to as "boy" by white people. Most music was not as explicit about racial themes as this song, but many other songs had undercurrents of social unrest.
Since about the 1980s, rhythm and blues has often been used to describe any music style performed by African American musicians and geared primarily toward African American audiences. This encompasses a wide range of styles, from gospel and soul to rap. Contemporary R&B music continues to address themes of injustice in American society from both religious and secular perspectives.