"the secrecy of the confessional "

-The Catholic Encyclopedia: 

"Confession is the avowal of one's own sins made to a duly authorized priest for the purpose of obtaining their forgiveness....   Virtual confession is simply the will to confess even where, owing to circumstances, declaration of sin is impossible; actual confession is any action by which the penitent manifests his sin....   Public  confession, as made in the hearing of a number of people (e.g. a congregation) differs from private, or secret, confession which is made to the priest alone and is often called auricular, i.e., spoken into  the ear of the confessor....  Regarding the sins revealed to him in sacramental confession, the priest is bound to inviolable secrecy. From this obligation he cannot be excused either to save his own life or good name, to save the life of another, to further the ends of human justice, or to avert any public calamity. No law can compel him to divulge the sins confessed to him, or any oath which he takes--e.g., as a witness in court. He cannot reveal them either directly--i.e., by repeating them in so many words--or indirectly--i.e., by any sign or action, or by giving information based on what he knows through confession."