“Duty” is a term used in international trade and is generally interchangeable with the word “tariff.” It refers to a Customs or border tariff, tax, or charge imposed in connection with the importation or exportation of goods. Duties are a source of revenue for the government and are also used to protect domestic industries against foreign competition. Duties may be assessed as a numerical percentage of the value of the goods (an ad valorem rate), or as a fixed amount (a specific rate), or a combination of these two methods. National legislation may define “duty” to exclude tariffs on exports and certain other types of border charges. Countries participating in World Trade Organization agreements “bind” or fix duties at agreed to levels and are prohibited from increasing them. Bilateral and regional trade agreements may also provide for the reduction or elimination of duties. In addition, some countries apply preferential (lower or zero) duty rates to qualifying imports from developing countries.