Inverse secret

Something that everyone in a particular area, group, community, etc. (ex: a school, a dorm hall, a classroom) knows, and must keep "secret" from one person. Generally the opposite of a traditional secret.

John: Hey, make sure Kathader doesn't find out about the albums we're making about her.
Jim: Okay, I won't, can i talk to others though?
John: Sure, it's an inverse secret so you can talk about it to anyone.