What is meant by the seal of confessional?

Answer 1

The "seal of the confessional" is basically the obligation that the priest has to never reveal the contents of a Sacramental confession. This is so important that he will be excommunicated if it is discovered that he has not maintained this confidentiality. This is outlined in the following canons from the 1983 Code of Canon Law: Can. 983 §1 The sacramental seal is inviolable. Accordingly, it is absolutely wrong for a confessor in any way to betray the penitent, for any reason whatsoever, whether by word or in any other fashion. §2 An interpreter, if there is one, is also obliged to observe this secret, as are all others who in any way whatever have come to a knowledge of sins from a confession. Can. 984 §1 The confessor is wholly forbidden to use knowledge acquired in confession to the detriment of the penitent, even when all danger of disclosure is excluded. §2 A person who is in authority may not in any way, for the purpose of external governance, use knowledge about sins which has at any time come to him from the hearing of confession. Can. 1388 §1 A confessor who directly violates the sacramental seal, incurs a latae sententiae excommunication reserved to the Apostolic See; he who does so only indirectly is to be punished according to the gravity of the offence. §2 Interpreters and the others mentioned in can. 983 §2, who violate the secret, are to be punished with a just penalty, not excluding excommunication.

Answer 2

The seal of confession means that a Catholic priest is not allowed to reveal to anyone else anything they learn from you during a confession. They can't reveal it even if their life or someone else's is threatened. If the priest breaks this seal he is automatically excommunicated from the Church, unless the Pope, himself, decides to lift this. If the Pope does lift the excommunication, the priest must undergo a long period of penance and never be able to hear confessions again.