"Annuity": A series of monthly payments, payable as of the first day of each calendar month during the annuity payment period, the first payment to be made as of the first day of the calendar month coincidental with or next following the first day of the annuity payment period and the last payment to be made as of the first day of the calendar month in which the annuitant dies or the annuity payment period ends. An annuitant may authorize the board to deduct from the annuity, premiums due under any group hospital-medical insurance program which is sponsored or approved by any employer.
40 ILCS 5/15-118