R and B vs rhythm and blues

R and B and rhythm and blues both are nouns.

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

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

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

R and B (noun)	rhythm and blues (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