An apostille is a French word meaning certification. It is comonly used in the USA to refer to the legalization of a document for international use under the terms of the 1961 Hague Convention Abolishing the Requirement of Legalization for Foreign Public Documents. 

Background

The United States signed the Hague Convention in 1961 and since 1981 it abolished the requirement to legalize foreign public documents (only). This treaty provides for a simplified certification of public documents (including documents that have been notarized) to be used in countries that participate in this Convention. Documents to be used in these countries and their territories shall be certified by one of the officials in the jurisdiction in which the document (or translation) was carried out. Such official must be designated as competent to issue certifications by "Apostille" (this is usually issued by office of the Secretary of State of his/her counterpart) as providd by the 1961 Convention. In the USA this means that a translated document translated and notarized and has been certified with an apostille from the Secretary of State of the state in which the notary resides.

With this certification by the Hague Convention Apostille, the document is entitled to recognition in the country of intended use, and no certification by the U.S. Department of State, Authentications Office or legalization by the embassy or consulate is required. Documents requiring certifications with an apostille by the U.S. Department of State are those that have been signed by a federal official with the official Seal of that agency, American Consular Officer, Military Notary (10 USC 1044a) or Foreign Consul (Diplomat Officials must be registered with the Office of Protocol).