A common market refers to a group of countries that have a mutual agreement to allow free trade among them while also maintaining a common external tariff. Synonyms for the term may include economic union, single market, or internal market. Economic union describes a group of countries that have agreed to coordinate their economic policies to optimize their overall economic strength. A single market refers to a situation in which goods, services, capital, and people can move freely among countries comprising a particular region. The term internal market emphasizes the idea of a single market within a particular group of countries, while common market highlights the shared tariff arrangements among the trade partners.