"The charts were an important part of the musical landscape of the 1950s. Billboard had separate lists of top-selling records for different groups of people, known as charts. Billboard would measure record sales, radio airplay, and jukebox favorites. “Race records” in the 1940s was the chart for music marketed to African-American audiences, whereas the “pop” chart measured sales of music that was marketed to white audiences.
Between 1949 and 1950, the term “race records” was replaced by “rhythm and blues” (eventually shortened to R&B) but the concept remained the same. However, music from the R&B charts began to cross over into the pop charts as white audiences became interested in African-American music." - University of Maryland Libraries
But as hillbilly music became a commercial product in the 1920s, record labels began dividing their releases into “hillbilly records” and “race records,” under the presumption that consumers bought music according to their race. Many of the black performers on hillbilly records went uncredited or were even scrubbed from marketing images in favor of white stand-ins.
One of the fundamental received wisdoms of popular music history is that due to taste and Jim Crow, white folks made one kind of music (which became the roots of country and western) and black folks simultaneously made what the industry labeled "race music" (blues, gospel, rhythm and blues).