He already said, the one who has been to TE for long time(assume that he took min. 1yr stay for this), number of post(assume that he took min 500 posts for this), reputation(the reps that others gave you for your posts, and may be he also included the politeness, behaviour with other members, iTrader points if you have sold anything or if there is any anti thread for you by someone and it's validity or so)
I am regular at at least four other forums, one has 5k, another has 1k I think, another has 400 which is really very very low and I don't know about the fourth. 5k is ideal IMO at the bare minimum that is. Although, 1k is also good if you don't use it all the time.