In pectore

In pectore (Latin for "in the breast/heart"; pronounced /ɪn ˈpɛktɒrɛ/) is a term used in the Catholic Church to refer to appointments to the College of Cardinals by the Pope whose names are not publicly revealed (hence reserved by the Pope "in his bosom"). This right of the pope is rarely exercised, usually in circumstances where the pope wants to make a statement for later historians about the honour due a particular cleric, while not wanting to endanger that same cleric in his present circumstances of persecution.

Popes may choose to keep cardinals' identities secret out of consideration for:

Cardinals appointed in pectore are not necessarily informed of their status, and their cardinalate (seniority) is calculated from the time of appointment rather than the announcement of that fact. Such an appointee cannot function as cardinal until his appointment is publicly announced, which once done, includes eligibility to participate in papal conclaves. Should a pope fail to do so, the cardinalate of an appointee ceases upon the appointing pontiff's death. Four popes, Innocent X,Benedict XIV, Gregory XVI and Pius IX, were originally created as cardinals in pectore but all were published quite soon afterward.

Areas where it is believed that unnamed in pectore cardinals were appointed are the People's Republic of China and, before the fall of the Soviet Union and collapse of the Iron Curtain, in central and Eastern Europe.

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Wikipedia