Pory is correct about trolling. It is basically a thread that is based on irrational hatred such as "Ur all dum." The troll just wants to get as many posts in the thread as possible, he cares not for what you say. Normally he'll keep the thread alive by enticing you with further flames.

EDIT: Reviving dead threas is called "necroing" or "Forum Necromancy." Like a necromancer, you bring back dead threads with a post. Since this forum isn't the busiest, I will allow moderate necroing, provided the post that does the deed has some actual content and is not thinly veiled ++ery.