An "apostille" is a form of authentication/certification issued to documents for use in countries that participate in the Hague Convention of 1961. Apostille is to confirm the legal authenticity of any document. A list of countries that accept apostilles is provided by the US State Department.
Apostilles are affixed by Competent Authorities designated by the government of a state which is party to the convention.
A list of these authorities is maintained by the Hague Conference on Private International Law. Examples of designated authorities are embassies, ministries, courts or (local) governments.
An Apostille Certificate is official government Certificate printed or stamped onto the reverse side of a single page document or attached to multiple paged documents with green notary ribbon making it become one inseparable document. It authenticates the seal and or signature of the public official or authority such as a notary or registrar issuing the document.