As stated, the acronym is Rhythm 'n' Blues, first given as a genre to black music of the 40's and 50's which had blues elements, but was faster, and designed for dancing. Nowadays, R 'n' B is used as an umbrella term for urban black music, which is a little confusing. To my generation, R 'n' B is The Stones, to my fifteen year old daughter, it's Beyonce - don't ask me why, it just is!