This would refer to a loan that does not have any payment or reduction of the amount owed. An example would be a interest only loan, which is a loan where the monthly payments are a make-up of only interest, the debt is not reduced but usually has a balloon-payment at some point in time or the principle is paid when the loan collateral, your house for instance, is sold. All the payments made during the life of the liability are interest, the property is sold and that is when the liability is paid.