What defines a standing order?

A standing order is defined as an instruction given by an account holder to their bank to make regular, scheduled payments of a specified amount. This type of arrangement is commonly used to pay recurring bills, such as rent or subscription services, where the payment amount remains constant over time.

The key characteristic of a standing order is its regularity and the predetermined amount that does not change with each payment cycle. This makes option B the most accurate definition, as it captures the essence of how an account holder utilizes a standing order to facilitate routine transactions without needing to initiate each one individually.

Other options, while potentially related to banking or payments, do not capture the specific nature of standing orders. An agreement between two banks is more indicative of interbank transactions or arrangements rather than a standing order, a type of loan agreement pertains to borrowing rather than payment processing, and a service provided for one-time payments does not fit the recurring nature that defines a standing order. Thus, option B stands out as the correct choice based on contemporary banking practices and terminology.