Commercial mortgage-backed security

Commercial mortgage-backed securities (CMBS) are a type of bond commonly issued in American security markets. They are a type of Mortgage-backed security, but are backed by mortgages on commercial rather than residential real estate. CMBS issues are usually structured into multiple tranches, similar to CMOs rather than typical residential passthroughs etc.
Many American CMBS demonstrate less prepayment risk than other types of MBS thanks to the structure of commercial mortgages. Commercial mortgages often contain lockout provisions after which they are often subject to defeasance, yield maintenance and prepayment penalties to protect bondholders.
European CMBS typically has less prepayment protection. Interest on the bonds is usually floating, i.e. based on a benchmark (LIBOR/EURIBOR) plus a spread.
Main article: Mortgage-backed security
The following is a descriptive passage from the "Borrower Guide to CMBS" published by the Commercial Mortgage Securities Association and the Mortgage Banker's Association[1]:
Commercial real estate first mortgage debt is generally broken down into two basic categories: (1) loans to be securitized (“CMBS loans”) and (2) portfolio loans. Portfolio loans are originated by a lender and held on its balance sheet through maturity.
In a CMBS transaction, many single mortgage loans of varying size, property type and location are pooled and transferred to a trust. The trust issues a series of bonds that may vary in yield, duration and payment priority. Nationally recognized rating agencies then assign credit ratings to the various bond classes ranging from investment grade (AAA/Aaa through BBB-/Baa3) to below investment grade (BB+/Ba1 through B-/B3) and an unrated class which is subordinate to the lowest rated bond class.
Investors choose which CMBS bonds to purchase based on the level of credit risk/yield/duration that they seek. Each month the interest received from all of the pooled loans is paid to the investors, starting with those investors holding the highest rated bonds, until all accrued interest on those bonds is paid. Then interest is paid to the holders of the next highest rated bonds and so on. The same thing occurs with principal as payments are received.
This sequential payment structure is generally referred to as the “waterfall.” If there is a shortfall in contractual loan payments from the Borrowers or if loan collateral is liquidated and does not generate sufficient proceeds to meet payments on all bond classes, the investors in the most subordinate bond class will incur a loss with further losses impacting more senior classes in reverse order of priority.
The typical structure for the securitization of commercial real estate loans is a real estate mortgage investment conduit (REMIC). A REMIC is a creation of the tax law that allows the trust to be a pass-through entity which is not subject to tax at the trust level. The CMBS transaction is structured and priced based on the assumption that it will not be subject to tax with respect to its activities; therefore, compliance with REMIC regulations is essential. CMBS has become an attractive capital source for commercial mortgage lending because the bonds backed by a pool of loans are generally worth more than the sum of the value of the whole loans. The enhanced liquidity and structure of CMBS attracts a broader range of investors to the commercial mortgage market. This value creation effect allows loans intended for securitization to be aggressively priced, benefiting Borrowers.