A tariff is a tax or custom duty on an imported good. It can take one of two forms: (1) a tax per unit, known as a specific tariff, or (2) a tax based on the value of the good, known as an ad valorem tariff.
President Trump supports tariffs as a way of resorting American jobs lost due to massive trade deficits. Tariffs were used for most of American history to build economic strength.
In telecommunications, a tariff consists of documents filed by a common carrier describing its services and the payments to be charged for such services.