A Customs Union is an agreement between two or more countries to eliminate tariffs and trade barriers on goods traded among them. This arrangement allows member countries to treat each other as a single market, promoting free trade and economic cooperation. However, they also agree to impose a common external tariff on goods imported from non-member countries. By participating in a customs union, countries can enhance their economic efficiency and competitiveness. Examples of customs unions include the European Union (EU) and the Southern African Customs Union (SACU), which facilitate smoother trade and economic integration among their member states.