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A tariff rate uniformly applied by a common market or customs union, such as the European Community, to imports from countries outside the union. For example, the European internal market is based on the principle of a free internal trade area with a common external tariff (sometimes referred to in French as the Tariff Extérieur Commun (TEC)) applied to products imported from non-member countries.
Source: http://usinfo.state.gov/products/pubs/trade/glossac.htm#commonext
In a free trade area, countries maintain their own tariff structure vis-à-vis third parties.