An unpaid or unsettled account; an account with a balance that has not been ascertained, that is kept open in anticipation of future transactions. A type of credit extended by a seller to a buyer that permits the buyer to make purchases without a note or security and is based on an evaluation of the buyer's credit. A contractual obligation that may be modified by subsequent agreement of the parties, either by expressed consent or by consent implied from the conduct of the parties, provided the agreement changing the contractual obligation is based upon independent consideration.