rhythm and blues vs R and B

rhythm and blues and R and B both are nouns.

Word	Noun	Adjective	Verb	Adverb
rhythm and blues	Yes	No	No	No
R and B	Yes	No	No	No

As nouns, rhythm and blues and R and B are synonyms defined as:

rhythm and blues and R and B: a combination of blues and jazz that was developed in the United States by Black musicians; an important precursor of rock 'n' roll

rhythm and blues (noun)	R and B (noun)
a combination of blues and jazz that was developed in the United States by Black musicians; an important precursor of rock 'n' roll	a combination of blues and jazz that was developed in the United States by Black musicians; an important precursor of rock 'n' roll