A mortgage deed is a legally binding agreement, using property as collateral for a loan. When you purchase a home, you make payments on a home loan. The mortgage deed is the paperwork you sign that allows the lender to put a lien on the property until the loan is paid. When people say they make a monthly mortgage payment, they actually mean they make a monthly loan payment while the mortgage deed secures the property for the lender.
Once the loan has been paid in full- the lien release for mortgage deed is filed at the county property records office and releases the lender's interest in the property.
The mortgage deed is typically two pages or less. What it does is confirm by the signature of the purchaser(s) that they are accepting the terms of the mortgage, agreeing to pay the loan back as outlined and that they agree with the mortgage company's offer to fund the loan. Someone must witness the signing of the mortgage deed. Depending on the state in which the property will be recorded, the rules of that specific state determine whether a notary or a notary plus additional signature witnesses are required.