Final answer:
In the 2008-2009 financial crisis, the security created when mortgage holders form a pool of mortgages and sell shares or participation certificates in the pool is called a mortgage-backed security.
Step-by-step explanation:
In the context of the 2008-2009 financial crisis, the security described is called a mortgage-backed security.
When lenders sell their mortgages to financial companies, those mortgages are bundled together and sold as investment products to investors. These investment products are known as mortgage-backed securities. The investors receive a rate of return based on the payments made by borrowers on the mortgages in the pool.
However, during the financial crisis, it was revealed that some of these mortgage-backed securities were riskier than initially believed, leading to a collapse in the housing market and a subsequent financial crisis.