Your company gets an order. To make or deliver something. You work on that and deliver great work. The customer is satisfied. The invoice goes out the door. At that moment, that customer is a debtor. Every customer who owes you money and has an outstanding invoice is a debtor. Has a customer paid? Then he is no longer a debtor.
DEFINITION OF DEBTORS: CUSTOMERS TO WHOM YOU SEND INVOICES AND FROM WHOM YOU HAVE NOT RECEIVED PAYMENT YET.