It stands for commercial mortgage-backed security; A CMBS is a fixed-income security (investment, instrument, etc.) backed by mortgage loans on commercial real estate rather than residential properties (in which case, residential mortgage-backed securities (RMBS) are issued). This security constitutes an interest in a pool of commercial mortgages or more, which acts as collateral (for security purposes). It entails payments of principal and interest to the holders from revenue generated by a pool. The underlying commercial mortgages are posted as collateral for the payment by the issuer.

By origin, it is an ABS (asset-backed security) a type of mortgage-backed security (MBS) backed by commercial and multifamily mortgages rather than residential mortgages. In most cases, commercial mortgage-backed securities are issued by a special purpose entity (SPV)/ a special purpose entity (SPE) (a trust) as part of a securitization process or structured finance transaction.