The commission on a postal order is

The commission on a postal order is called "poundage." A postal order is a financial instrument that is issued by postal services in many countries. It is similar to a check or money order, but is generally considered to be a safer and more secure method of payment. When purchasing a postal order, the buyer typically pays an additional fee or commission to cover the cost of issuing and processing the order. This fee is known as "poundage." Poundage is generally a percentage of the total value of the order, and can vary depending on the country and the specific postal service. The other options listed - tariff, brokerage, and fee - all refer to different types of charges or fees that may be associated with financial transactions, but they are not specifically related to postal orders. For example, a tariff is a tax or duty that is imposed on imported or exported goods, while brokerage refers to the fee charged by a broker for arranging a financial transaction.