A security representing an ownership interest in an underlying pool of mortgages. The cash flow from the underlying mortgages is “passed through” to the security holder as monthly payments of principal, interest, and prepayments. Pass-through securities have been guaranteed and issued by the Government National Mortgage Association (GNMA), the Federal National Mortgage Association (FNMA or “Fannie Mae”), and the Federal Home Loan Mortgage Corporation (FHLMC or “Freddie Mac”), as well as private institutions.