Tariff
A tariff is a tax on imports or exports between sovereign states. It is a form of regulation of foreign trade. It is a policy that taxes foreign products to encourage or protect domestic industry. It helps limit trade deficits. The tariff is historically used to protect infant industries and to allow import substitution industrialization.
Tariff
An externality is the term used when the price of a product does not reflect its cost or real economic value. The classic negative externality is environmental degradation, which reduces the value of natural resources without increasing the price of the product that has caused them harm. The classic positive externality is technological encroachment, where one company's invention of a product allows others to copy or build on it, generating wealth that the original company cannot capture. If prices are wrong due to positive or negative externalities, free trade will produce sub-optimal results.