In the context of mailing lists, discussion groups, discussion forums, bulletin boards, newsgroups, and wikis a contribution is off-topic if it is not within the bounds of the current discussion, and on-topic if it is.
Even on very specialized forums and lists, off-topic posting is not necessarily frowned upon,1 but a common netiquette convention is to mark a new off-topic posting or email by beginning it with "OT"2 - for example in a forum discussing the Linux operating system someone might post: "OT: Did anyone else see that giant goose?".
Posting off-topic messages to deliberately aggravate other members is a form of trolling.
References
References
- "Members of more informal lists may be excited to learn you've had a baby or landed a new job. Others may find such posts annoying and may even flame you. " Archived 2016-03-04 at the Wayback Machine, Medieval Mailing Lists
- "It is appreciated if articles that have absolutely nothing to do with Tolkien have subject lines beginning with "OT:" ("Off Topic")." Archived 2021-01-25 at the Wayback Machine. The Tolkien Newsgroups FAQ