The term "Rhythm and Blues" was coined by Jerry Wexler (who went on to be a famous record company executive and producer) when he was working as a journalist at *Billboard* Magazine, circa 1952. ([Wikipedia link][1]). *Billboard* had a weekly chart displaying the popularity of single recordings played on radio stations with an African-American audience, and it the chart was called "Race" (as in "racial"). Recordings made by and marketed and sold to African-Americans had previously been called "race records". Wexler proposed the name "Rhythm and Blues" at a staff meeting of *Billboard* magazine when they discussed wanting to change the name of the "Race" chart to something else.

As was mentioned earlier, influential radio personality Alan Freed coined the term "rock and roll".

For the most part, in popular usage in the United States of America, "rock and roll" refers to recordings recorded by white musicians and marketed and sold to a white audience. "Rhythm and Blues" refers to popular music of the day that was recorded by African-American musicians and marketed and sold to an African-American audience.

Note that the key to this is the term "marketed and sold". Both "Rock and Roll" and "Rhythm and Blues" were more or less designations created by the commercial music industry to describe how the music was marketed and sold, and to whom it was marketed.

Notwithstanding, there came to be distinct artistic characteristics of each kind of music.


  [1]: http://en.wikipedia.org/wiki/Jerry_Wexler#Career