A blanket mortgage is a single mortgage that covers two or more pieces of real estate. The entire bundle of real estate is held together as the collateral but you can sell individual properties without having to get rid of or retire the existing mortgage.
These kinds of mortgages are popular for developers, flippers, and real estate investors. They let you have more cash on hand and to save time. You can save on the costs associated with applying for and closing on multiple mortgages at once.
In a blanket mortgage, the entire real estate bundle is the collateral. The entire group of assets serves as the collateral, in this case, than the individual properties themselves.