Securitization is the fancy title for the selling of a pool of assets to a trust, which turns around and finances the purchase by selling securities to the market. These securities are backed by the original assets.
An investor who purchases company stock has a claim to the company’s assets and future cash flows. Similarly, an investor who purchases a securitized debt product has a claim against the future repayment of the underlying debt instruments (which is an asset in this case).
