A tariff is a customs duty or tax levied on imports of merchandise goods. Most of the time a tariff is an ad valorem tariff (percentage of value) or a specific tariff (e.g. $100 per ton). Less often, it can be a compound tariff made up of both of these elements applies. Tariffs are mostly levied on imports, but there are cases of tariffs on exports. Tariffs raise revenue for the government and increase the prices of imported products, thus giving domestically produced products a price advantage.