CDO (Collateralized Debt Obligation) collateralized debt obligations, it is the market to make up for ABS (real estate-backed securities loans) less than, and has created out of the credit products it is most characteristic of the structure to provide themselves through their own "credit enhancement", that is usually a secondary series (Subordinated Tranche) or an equity line (Equity Tranche or Income Notes), from these series to act as a buffer when the CDO asset credit problems, the first series loss of the equity and subordinated Series (equity Series held by the issuer's own).