Final answer:
Billboard replaced the term 'rhythm and blues' with 'R&B' to label African American popular music for various reasons, including the need for a more modern and marketable term and to break down racial barriers.
Step-by-step explanation:
Billboard replaced the term 'rhythm and blues' with 'R&B' to label African American popular music for several reasons. First, 'rhythm and blues' was seen as a dated term that did not reflect the evolving sound and style of the music. Second, 'R&B' was shorter and catchier, making it more appealing and marketable.
Finally, the term 'rhythm and blues' had been associated with a segregationist mindset, and using 'R&B' helped to break down racial barriers by making the music more accessible and inclusive.