Specified number of years during which a benefit is guaranteed to continue. In a period certain pension plan, for example, the participant (or his or her beneficiary) is paid a certain sum for (depending upon the period specified) 5, 10, 15, or 20 years, even if the participant dies. If the participant outlives this period, no further sum is paid unless it is a 'life income period certain' plan or annuity. The amount paid in a period certain plan is normally more than that for the life income period certain plan because the total amount to be paid is known in advance.