Asset Backed Securities (ABS) are financial securities backed by a pool of assets that produce income, generally loans. In the case of Mortgage Backed Securities (MBS) and Commercial Mortgage Backed Securities (CMBS), the underlying assets are, respectively, residential and commercial mortgages. However, unlike MBS, asset backed securities are backed by non-mortgage loans, including auto loans, student loans, credit card debt, and variety of other types of debt. Therefore, it could be argued that the structural differences between ABS, MBS, and CMBS are mostly superficial-- it is only the exact type of loan that changes.
In general, to create an mortgage backed security, like a CMBS, the initial lender will sell the loans to a trust, which is typically set up as a special purpose entity (SPE), or special purpose vehicle (SPV), in order to pool the loans together and issue them to investors. Other major creators of MBS products include Ginnie Mae (the Government National Mortgage Association), which securities government-insured loans, including many HUD/FHA-insured single-family and multifamily loans. Other prominent MBS issuers include Fannie Mae and Freddie Mac which are both GSEs (government-sponsored enterprises).
In a similar fashion, asset backed securities also are created by pooling assets into a trust. For instance, a credit card company, such as Capital One, will pool unpaid credit card debt into a trust, which will issue semi-regular payments to investors who purchase shares. The same can be said for auto loans, student loans, and other loan products that are securitized into ABS.