A shared-appreciation mortgage (SAM) is a type of mortgage in which the lender agrees to accept a lower interest rate in exchange for a share of the appreciation in the value of the property. This means that if the value of the property increases over time, the lender will receive a portion of that increase. SAMs are often used as a way for borrowers to get a lower interest rate, but it also means that the lender will share in the upside if the property increases in value.