A collateralized debt obligation is a complex structured finance product that is backed by a pool of loans and other assets. These underlying assets serve as collateral if the loan goes into default. The tranches of CDOs indicate the level of risk in the underlying loans, with senior tranches having the lowest risk.

A collateralized mortgage obligation (CMO) refers to a type of mortgage-backed security that contains a pool of mortgages bundled together and sold as an investment. Organized by maturity and level of risk, CMOs receive cash flows as borrowers repay the mortgages that act as collateral on these securities.

Typically, retail investors can't buy a CDO directly. Instead, they're purchased by insurance companies, banks, pension funds, investment managers, investment banks, and hedge funds. These institutions look to outperform the interest paid from bonds, such as Treasury yields.

What Is the Difference between Collateralized Debt Obligations (CDOs) and Mortgage-Backed Securities (MBS)? MBS are investments marketed as securities, which entails bundling a set of mortgages. CDOs are investments marketed as securities, which includes a bundle of assets such as bonds, loans, and mortgages.