Although the Holy See is sometimes metonymically referred to as the "Vatican", the Vatican City State was distinctively established with the Lateran Treaty (1929) between the Holy See and Italy to ensure the temporal, diplomatic, and spiritual independence of the Papacy. As such, ambassadors are officially accredited to the Holy See and not the Vatican City State. Conversely, Papal nuncios to states and international organisations are recognised as representing the Holy See and the integrity of the Catholic Church along with its 1.3 billion members, not the Vatican City State, as prescribed also in the Canon law of the Catholic Church (1983). The "Holy See" thus refers to the See of Rome viewed as the central government of the Catholic Church. The Catholic Church, in turn, is the largest non-government provider of education and health care in the world, while the diplomatic status of the Holy See facilitates the access of its vast international network of charities.
Every see is considered holy. In Greek, the adjective "holy" or "sacred" (ἱερά transliterated as hiera) is constantly applied to all such sees as a matter of course. In the West, the adjective is not commonly added, but it does form part of an official title of two sees: besides the Diocese of Rome ("the Holy See"), the Bishopric of Mainz (the former Archbishopric of Mainz, which was also of electoral and primatial rank) bears the title of "the Holy See of Mainz" (Latin: Sancta Sedes Moguntina).