815 ILCS 405/2.7

"Retail charge agreement" or "charge agreement" means an instrument prescribing the terms of a retail installment transaction which is made pursuant to the instrument, whether secured or unsecured, in which the buyer's total unpaid balance under the instrument is payable in one or more installments over a period of time and under the terms of which the finance charge is to be computed in relation to the buyer's unpaid balance from time to time.