Rhythm and Blues (which can be shortened to R&B) is a genre of music that has mainly been performed by African-Americans since the late 1930's.
The history of R&B
"Race music" was an offensive term that was previously used to describe music created by black people, until Billboard began to use the term "Rhythm and Blues" as it was deemed more appropriate. This genre of music, in the 1950's, was viewed as a less artistic version of jazz, and as Hip Hop began to dominate balck culture, it was dismissed as a bunch of love songs. Later on, in the 1970's, R&B became a term that was used to describe both soul and funk forms of music, and is presently widely used to describe urban music created by black people.