From the longer Wikipedia, page 
The Vatican Secret Archives (Latin: Archivum Secretum Vaticanum), located in Vatican City, is the central repository for all of the acts promulgated by the Holy See. The Pope, having primal incumbency until death, owns the archives until the next appointed Papal successor. The archives also contain the state papers, correspondence, papal account books, and many other documents which the church has accumulated over the centuries. In the 17th century, under the orders of Pope Paul V, the Secret Archives were separated from the Vatican Library, where scholars had some very limited access to them, and remained absolutely closed to outsiders until 1881, when Pope Leo XIII opened them to researchers, more than a thousand of whom now examine its documents each year.
The use of the word "secret" in the title "Vatican Secret Archives" does not denote the modern meaning of confidentiality. Instead, it indicates that the archives are the Pope's personal property, not belonging to those of any particular department of the Roman Curia or the Holy See. The word "secret" was generally used in this sense as also reflected in phrases such as "secret servants", "secret cupbearer", "secret carver", much like an esteemed position of honour and regard comparable to a VIP.
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