drift alert...

I agree with Richard Bridge that the current (or perhaps "a" current) usage of the label "RnB" is entirely incorrect. Some current commentators seem to use this term to describe any and all music marketed to the African-American public which is neither rap/hip-hop nor gospel ~ that is, the term is used to classify contemporary ballads, generally heavy with synthesized strings, which is neither rhythmic nor particularly "bluesy."

Historical usage of RnB/R&B refers to a genre of music that first appeared just after World War II in the black community. It was around that time that the title for the Billboard chart intended to tracks sales of such records was changed from "Race Records" to "Rhytm and Blues." At the same time, the availability of amplification, and especially of the electric guitar, made it economically possible (if not imperative) that touring bands now consist of a half-dozen or fewer musicians, not a full "big-band" complement of players. All you needed now to entertain a loud barrom crowd was an electric guitar, bass and drums, plus maybe a single saxophone and/or an elctric organ.

Examples of the music orignally called R&B include the works of Louis Jordan, Big Joe Turner, the less-widely-known Professor Longhair, Huey Piano Smith, Guitar Slim, etc., etc. This music (surprisingly, to some) found an audience among younger white folk, and was soon renamed "rock and roll" (presumably to eliminate the previous racial identification).

Now that "rock and roll," and even the slightly-more-specific "rock," have become very broad categories that include plenty of music that lacks the "roots"/blues intensity of the original stuff, I tend to use the term "R&B" (if only in my own mind, if not publicly) to classify a type of music that I like much more than I like the contemporary black-easy-listening genre that some folks now call "RnB."

Incidentally, my own feeling is that "real" R&B, and specifically 1950s-60s New Orleans R&B as recorded in Cosimo Matassa's studio by the likes of Little Richard, Ray Charles, Fats Domino, the aforementioned Professor Longhair and Huey Smith, et al, is the true successor to the original "trad" jazz music born in N.O. ~ at least as validly, if not moreso, than the cerebral music of Miles Davis, John Coltrane and others and their successors. The first jazz music was dance music ~ physical booty-shaking music ~ and players schooled in jazz provided the backbone of those early R&B recordings. "Modern jazz," on the other hand, is intended to be heard in a polite, meditative manner, with the audience sitting still and listening quietly. Good music, certainly, but not the rowdy good-time sound that Buddy Bolden, Kid Ory, Sidney Bechet, and Satchmo originally had in mind...