Today, your local commercial bank is offering a one-year CD with an interest rate of 3%, so the existing one-year risk-free rate is 6%. You notice that Metallica Financial Company offers an interest rate of 7% on one-year certificates. The risk premium offered by this certificate is RP = R - Rf = 7% - 3% = 4%

I just want to know what the letters in the formula stand for.

For example:

RP=R - Rf

What do RP, R, and Rf mean? in words. I used the problem above for reference but doesn't need to be solved.