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.
Common external tariff
A common external tariff must be introduced when a group of countries forms a customs union. The same customs duties, import quotas, preferences or other non-tariff barriers to trade apply to all goods entering the area, regardless of which country within the area they are entering. It is designed to end re-exportation; but it may also inhibit imports from countries outside the customs union and thereby diminish consumer choice and support protectionism of industries based within the customs union]]
The common external tariff is a mild form of economic union but may lead to further types of economic integration. In addition to having the same customs duties, the countries may have other common trade policies, such as having the same quotas, preferences or other non-tariff trade regulations apply to all goods entering the area, regardless of which country, within the area, they are entering.