what does META mean.

Um, it's Greek. As in, been in use for thousands of years, and means many things in many contexts. While we're actually seeking knowledge, might as well pretend to get it right. It means derivative or about something, rather than the thing itself.

In the context of games and gaming, it has more recently come to refer to discussion of optimum performance and the means of achieving it -- ie, about the game rather than the game itself. Hence "meta" as either noun or adjective refers to current thinking (including the assumption that it is rapidly changing) regarding the most efficient or optimum build for said game. So, saying some thing or another is "meta" in this context means that folks think it is either itself, or an integral part of a strategy that constitutes, state-of-the-art and "best" given the presently-available in-game options. (This, inevitably, incorporates an extensive analysis of potential in-game scenarios, counters, and so forth. This process, deep consideration of potential scenarios stemming from a rule set rather than the rules or game itself, could be said to be "very meta.")

There you go.