R and B vs popular music genre

R and B and popular music genre both are nouns.

Word	Noun	Adjective	Verb	Adverb
R and B	Yes	No	No	No
popular music genre	Yes	No	No	No

As nouns, popular music genre is a hypernym of R and B; that is, popular music genre is a word with a broader meaning than R and B:

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
popular music genre: any genre of music having wide appeal (but usually only for a short time)

Other hypernyms of R and B include African-American music, black music, popular music.

R and B (noun)	popular music genre (noun)
a combination of blues and jazz that was developed in the United States by Black musicians; an important precursor of rock 'n' roll	any genre of music having wide appeal (but usually only for a short time)