As an independent sovereign entity, holding the Vatican City enclave in Rome as an independent state, it maintains diplomatic relations with other states. It is viewed as analogous to a state while administered by the Roman Curia (Latin for Roman Court), similar to a centralised government with the Cardinal Secretary of State as its chief administrator, and various dicasteries, comparable to ministries and executive departments.
Diplomatically, the Holy See acts and speaks for the whole church. It is also recognised by other subjects of international law as a sovereign entity, headed by the Pope, with which diplomatic relations can be maintained. Although it is often informally referred to as "the Vatican", the "Holy See" is not the same entity as the "Vatican City State", which came into existence only in 1929 because of the Lateran Treaty; the Holy See, the episcopal see of Rome, dates back to antiquity. Ambassadors are officially accredited not to the Vatican City State but to "the Holy See", and Papal representatives to states and international organizations are recognized as representing the Holy See, not the Vatican City State. The creation of the Vatican City State was meant to ensure the diplomatic and spiritual independence of the Pope.
The expression "the Holy See" (without further specification) is normally used in international relations (and in the Canon law of the Catholic Church) to refer to the See of Rome viewed as the central government of the Catholic Church.
The word "see" comes from the Latin word "sedes", meaning "seat", which refers to the Episcopal throne (cathedra). The term "Apostolic See" can refer to any see founded by one of the Apostles, but, when used with the definite article, it is used in the Catholic Church to refer specifically to the see of the Bishop of Rome, whom that Church sees as successor of Saint Peter, the Prince of the Apostles. While Saint Peter's Basilica in Vatican City is perhaps the church most associated with the Papacy, the actual cathedral of the Holy See is the Archbasilica of Saint John Lateran within the city of Rome.
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).