40 ILCS 5/12-125

"Reversionary annuity": A deferred annuity computed according to the applicable actuarial table, based on employee and employer contributions for surviving spouse's service annuity and surviving spouse's prior service annuity, and payable to the beneficiary during lifetime, or other stated period, only if the beneficiary survives the employee receiving a retirement annuity and qualifies as the surviving spouse under Section 12-123.1.