An Open Loop Credit Card is a credit card that be used just about everywhere. These cards have a Visa, Master Card, America Express, or etc., logo on it. They are you normal everyday credit cards that came be used at just about every and any store.
Closed Loop credit cards, however, are cards that are issued by one store and can only be used at only that one particular store. This are credit card that are normally issued by a major nation wide retailer.
Click for the full glossary of credit card terms.