A
collateralized mortgage obligation that seeks to protect
investors from
prepayment risk. PACs do this by setting a schedule of payments; if prepayments of the
underlying mortgages exceed a certain rate, the life of the PAC is shortened. If they fall below a certain rate, the life of the
tranche is extended. This helps protect investors in case the
holders of the underlying mortgages do not pay off their mortgages as expected.