It has two main meanings.
The primary one is when somebody posts a duplicate thread. This term came about one day when Rico Fata was placed on waivers, and there was a barrage of threads about it.
The second (and lesser used) meaning is in place of the "F" word. On the old forum software we had it programmed to replace the "F" word with fata automatically- and some of us old timers use it in place of the "F" word.
Edit- and it looks like I've been fata'd in the Fata thread.
