What is the meaning of Junk bond?

Junk bonds carry a higher-than-average risk of default, which means that the bond issuer may not be able to meet interest payments or repay the loan when it matures. Except for bonds that are already in default, junk bonds have the lowest ratings, usually Caa or CCC, assigned by rating services such as Moody's Investors Service and Standard & Poor's (S&P). Issuers offset the higher risk of default on junk bonds by offering substantially higher interest rates than are being paid on investment-grade bonds. That's why junk bonds are also known, more positively, as high-yield bonds.