Necro'd threads are threads that have been inactive for a few months or more. Most of the time necro'ing a thread is not advised as it can conjure up old arguments (read: feuds) that are better left alone. Depending on the circumstances we'll allow a necro'd thread to stay open. Just depends on context. IE: Update vs renewing an argument vs whether the subject matter is still being discussed in other areas of the forum etc etc. (this is by no means an exhaustive list of what determines why a necro'd thread is left open or closed.)

Needless to say, we generally prefer that posters start new threads. So if you want to really discuss whatever it is you wish to discuss it'd be best if you just start a new thread instead of necro'ing an old thread.