Rhythm and Blues, or R&B, is a musical marketing term introduced in the late 1940s by Billboard magazine to replace the term race music, which was deemed offensive. Rather than describing a recognizable musical genre, rhythm and blues has come to be used to indicate whatever contemporary music is popular with African-Americans.
In its first manifestation, rhythm and blues was a black version of a predecessor to rock and roll. It was strongly influenced by jazz and jump music as well as black gospel music, and influenced jazz in return (hard bop was the product of the influence of rhythm and blues, blues, and gospel music on bebop). Musicians paid little attention to the distinction between jazz and rhythm and blues, and frequently recorded in both genres. Numerous swing bands (for example, Jay McShann's, Tiny Bradshaw's, and Johnny Otis's) also recorded rhythm and blues. Even a bebop icon like arranger Tadd Dameron also arranged for Bull Moose Jackson and spent two years as Jackson's pianist after establishing himself in bebop.
Ironically, it was through the thriving UK pop scene of the early 1960s that R&B reached the height of its popularity. Without the same kind of racial distinctions that refused it acceptance in the USA, white British performers and listeners adopted this novel style of music without question, and groups such as The Rolling Stones and Manfred Mann brought it to a wider audience.
The term fell into disfavor in the 1960s being replaced by soul music and Motown, but has re-emerged in recent years indicating black popular music encompassing pop heavily influenced by hip-hop, funk, and soul music. In this context only the abbreviation R&B is used, not the full expression.