The Vatican
The Vatican is the hill in Rome where Saint Peter is supposed to have been martyred in 65AD. A basilica dedicated to him was built on the site, and the successors of St Peter (the Popes) took up residence in the area.
The Vatican City is an independent State, with its own diplomatic corps. The Vatican City houses the administrative offices of the worldwide Catholic Church, otherwise known as the Holy See, as well as the Basilica of St Peter, the Papal residence and the Vatican museums.
The term "The Vatican" is often used to refer to the administration of the Church.
The Roman Curia is the central administration of the Church, based in the Vatican. It consists of:
Secretariat of State - general affairs of the Church and the Vatican "Foreign Office"
Congregations
Tribunals
Pontifical Councils
Synod of Bishops
Offices
Pontifical Commissions
Swiss Guard
Institutions Connected with the Holy See
Labour Office of the Apostolic See
Pontifical Academies
Pontifical Committees