Fannie Mae (FNMA) – The nickname for Federal National Mortgage Association. Fannie Mae is a federally chartered, shareholder-owned company that is the nation’s largest source of financing for home mortgages. They purchase residential mortgages, then sell and insure securities, called Mortgage-Backed Securities (MBS), based on those mortgages to investors. Loans that fall within Fannie Mae's underwriting guidelines, and therefore may be bought and securitized by Fannie Mae, are called conforming loans.