It stands for conditional prepayment rate or constant prepayment rate; the annualized percentage of an existing mortgage pool that is expected to be prepaid in a year. It is an annual rate at which a mortgage (loan) pool balance. It is the annual rate at which a mortgage pool balance is estimated to be prepaid during the life of the pool. This assumes a constant percentage of mortgages or similar loans will be prepaid during the set timeframe.

The percentage of outstanding mortgage loan principal is repaid based on the annualization of the single monthly mortality (SMM), which reflects the outstanding mortgage loan principal that is repaid on a monthly basis. A constant amount of the outstanding loans will be repaid each month.