Customs duty

A tax levied on imported goods, on the basis of a tariff.

A tariff schedule is a document specifying the rates of duty to be applied on various imported products.
Customs duties are "levied either on an ad valorem basis (percentage of value) or on a specific basis (e.g. $7 per 100 kg). Tariffs give a price advantage to similar locally-produced goods and raise revenues for the government."
(World Trade Organization (WTO), Tariffs, visited 2010-11-01)