Apostille
The Apostille is a certificate with a seal/stamp which certifies (legalizes) a document from the country where the document was issued.
Documents bearing an Apostille are exempted from any further form of legalization in countries that are members of the 1961 Hague Convention (see question: Which countries are members of the Hague Convention on Abolishment the Requirement of Legalisation for Foreign Public Documents?).