An investment grade bond backed by a pool of bonds with differing degrees of credit quality.
An investment-grade bond backed by a large, diversified pool of junk bonds. Usually broken down into tiers with varying degrees of risk and varying interest rates.
Investment-grade bonds backed by a collection of junk bonds with different levels of risk, called tiers, that are determined by the quality of junk bond involved. CBOs backed by highly risky junk bonds receive higher interest rates than other CBOs.