I said I wasn't going to get into definitions, but I feel the need to say this-the term "rhythm records" which is used in that quote I posted is a euphemism for "race records". And "race records" is a euphemism for "Black American non-religious music".

See this excerpt from this Wikipedia page http://en.wikipedia.org/wiki/Race_music

"Race music is the term used in the first half of the 20th century for the kinds of African American music of that time, like jazz, boogie-woogie, blues, jump blues, and rhythm-and-blues. Robert Palmer described it as "urbane, rocking, jazz based music with a heavy, insistent beat".

From 1942 to 1945 the Billboard category for this music was called the Harlem Hit Parade, and was changed in 1949 to Race records. In 1948 RCA Victor was marketing black music under the name Blues and Rhythm, but it was not until 1958 that the term Rhythm and Blues replaced the Billboard category Race records."