A debtor is a person or enterprise that owes money to another party. (The party to whom the money is owed is often a supplier or bank that will be referred to as the creditor.)
A creditor is a person, bank, or other enterprise that has lent money or extended credit to another party. (The party to whom the credit has been granted is often a customer that will now be referred to as a debtor.)
If Company X borrowed money from its bank, Company X is the debtor and the bank is the creditor. If Supplier A sold merchandise to Retailer B, then Supplier A is the creditor and Retailer B is the debtor.