Necroposting
Replying in a thread that has been dead for seven years — irritating on a forum, invaluable on Stack Overflow.
Reviving an old discussion by posting in it, which pushes it back to the top. On traditional forums this counts as a breach of netiquette: the participants have moved on, the context is gone, and whoever answers a question from 2011 is often answering someone who stopped logging in around 2013.
On search-driven sites the judgement is the opposite. An old Stack Overflow question is the result people will land on for the next ten years, and an answer describing how the problem is solved in the current version is worth more than the whole original thread. The difference lies in whether the platform is a conversation or a reference work — and most arguments about necroposting are really about the two sides assuming different answers to that.