Why is the Vatican sometimes called the “Holy See"?
A little background in ecclesiology will help explain why we call the Vatican the Holy See. The Church is very structured and organized in its hierarchy. A diocese is a geographic area governed by a bishop appointed by the Pope. Each diocese is further broken down into parishes, which have pastors who represent the bishop in his teaching authority.
The diocese of Rome has a particular role in the Church because of its importance and antiquity. The Pope is head of the Church because he is the Bishop of Rome. Every bishop has a seat or throne, which is the symbol of his teaching authority and is located in the cathedral of each diocese. The Latin word for seat is “sedes.” So each diocese can be referred to as a “see.” Most people think that St. Peter’s is the cathedral of Rome, but St. John Lateran Basilica is actually the cathedral of the Archdiocese of Rome. This is where the Pope’s seat or throne as Bishop of Rome is found. So, the Holy See is a reference to the chair of Peter, the Pope’s Chair.