Anibal Jose Baez
A remittance advice is a letter sent by a customer to a supplier, to inform the supplier that their invoice has been paid. If the customer is paying by cheque, the remittance advice often accompanies the cheque. The advice may consist of a literal letter (e.g., "Gentlemen: Your shipment of the 10th inst was received in good order; accompanying is our remittance of $52.47 per invoice No 83046") or of a voucher attached to the side or top of the cheque.
Remittance advices are not mandatory, however they are seen as a courtesy because they help the accounts-receivable department[4] to match invoices with payments. The remittance advice should therefore specify the invoice number(s) for which payment is tendered.
http://en.wikipedia.org/wiki/Remittance_advice