Mandatory delivery commitment: An agreement that a lender will deliver loans or securities by a certain date at agreed-upon terms.

Margin: an amount the lender adds to an index to determine the interest rate on an adjustable rate mortgage.

Medium-term notes: Unsecured general obligations of Fannie Mae with maturities of one day or more and with principal and interest payable in U.S. dollars.

Modification: Any change to the original terms of a mortgage.

Mortgage: A legal document that pledges property to a lender as security for the repayment of the loan. The term also is used to refer to the loan itself.

Mortgage-Backed Security (MBS): A Fannie Mae security that represents an undivided interest in a group of mortgages. Principal and interest payments from the individual mortgage loans are grouped and paid out to the MBS holders.

Mortgage banker: a company that originates loans and resells them to secondary mortgage lenders like :Fannie Mae or Freddie Mac.

Mortgage broker: a firm that originates and processes loans for a number of lenders.

Mortgage insurance: a policy that protects lenders against some or most of the losses that can occur when a borrower defaults on a mortgage loan; mortgage insurance is required primarily for borrowers with a down payment of less than 20% of the home's purchase price.

Mortgage insurance premium (MIP): a monthly payment -usually part of the mortgage payment - paid by a borrower for mortgage insurance.

Mortgage Modification: a loss mitigation option that allows a borrower to refinance and/or extend the term of the mortgage loan and thus reduce the monthly payments.

Multifamily housing: A building with more than four residential rental units.