So you are a forum member and you are reading some old threads. Suddenly you see an extremely interesting thread, maybe a few months old, sometimes even years old. You like it, you don't understand why it was abandoned... You want to revive it.
While some forums explicitly ask people to revive old topics instead of posting a new-but-similar one, other communities can and often will get pissed if someone starts digging up a number of ancient threads and parading the shambling corpses around. The threads died for a reason, after all, and dragging them back up without providing something new to add (and have other people discuss) will inevitably lead to the forumites grabbing the Torches and Pitchforks. They may also end up awakening something that was not meant to be awakened, especially if the thread was killed by a nasty Flame War. The hapless necromancer may raise the topic from the depths hoping to rekindle the original discussion only to have it burst into flames as the tangent reignites the posters. In particularly extreme, though not uncommon, cases of Thread Necromancy, a newbie will wind up attempting to strike up a conversation with someone who doesn't even visit the forum anymore.
There are three exceptions to the above:
- First, the hostile revival. Much like in real life arguments, you will often think of the perfect insult hours, days or even weeks after the argument in which it could be used has ended. In forums, though, you don't lose this opportunity, and those still simmering over the issue will bring back an argument specifically to post their belated assault. These individuals are rightly reviled, as they end up bringing back old hostilities best left undisturbed for the sole reason of self-gratification.
- Second is the Story thread, where an author posts a story as a thread in order to get commentary on the story (common in certain kinds of message boards, particularly for Fan Fiction). Anybody bumping the thread months after the fact in hopes of getting more: one, probably isn't going to get it, and two, can expect cries of rage from people who liked the story and were taunted by the post which got their hopes up of a new installment (if you actually do have a new installment, however, it's generally fine to revive the thread).
- Third is the Roleplay thread, in case a Roleplay thread had no participant or people left it inactive for weeks, the host may occasionally bump it to either allure the other to join or to remind the other players. Sometimes the players would demand the Thread Necromancer to revive it. This is a rare occasion which a Thread Necromancer can become beneficial.