Lulz
Lulz is a corruption of LOL, which stands for laugh out loud. Lulz are the reason for Anonymous's existence; everything Anonymous does is for the lulz. Truly epic lulz come from raids and invasions. Habbo Hotel and MySpace seem to provide an endless source of lulz to Anonymous, but raids of smaller websites and forums seem to have a much more limited shelf life. Regardless, "doing it for the lulz" is considered sufficient justification for any action, no matter how perverse and offensive. Unfortunately the FBI disagrees, so /b/tards in pursuit of the lulz must always beware the 4chan Party Van.
Lulz enjoys an interesting history for a fairly straightforward meme. MySpace and Xanga users really do spell LOL "lolz" and for this reason saying "lulz" made you sound borderline retarded even in jest, and people who used it were frowned upon and called newfags. Similarly, Something Awful users were banned just for using the term. The only place where it was commonly used was Encyclopedia Dramatica. However, after the FOX11 video "lulz" gained enough irony to become a truly funny meme and it entered the 4chan mainstream.