Credit ratings are evaluations of a borrower's ability to repay debt. They're given by credit rating agencies and range from AAA (best) to D (worst). AAA indicates an extremely low risk of default, AA very low risk, A low risk, BBB moderate risk, and BB, B, CCC, CC, C high risk (known as 'junk' ratings). D indicates that the borrower has already defaulted on their debt. Credit ratings signal the risk level of an investment by reflecting the issuer's financial health, payment record, and debt terms. While not guarantees, they are trusted indicators of credit risk for investors.