QUESTION: What exactly is the seal of the confessional?
I've heard a priest describe a sin, and say that they weren't willing to absolve it. Isn't that something to be kept private?
Answer: The seal of confession is:
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. (Code of Cannon Law)
It is hard to comment further without the facts but if the priest was stating a general instance that he couldn't forgive the sin, then there is nothing wrong with that. Especially, if he is using it to educate others on how to better form their lives to Christ.