Short for “meta gaming” or “meta game”, which is essentially the identification and application of the various playing style archetypes that work best in any given game.

As others have said, it functionally means picking the most optimal strategies and/or equips, but it’s now somewhat archaic use was more like a scholarly examination/application of archetypes, playstyles, use-cases, and vulnerabilities/bugs/eccentricities that could be taken advantage of and brought together to make consistent winning strategies. There is rarely ever (probaly never, really) a meta that stays unchanged throughout its games history because meta is, in a way, an ever-ongoing conversation between the game, its players and, in some ways, the wider audience that both bring in.

Well balanced games with deep design choices often have sleeper strategies that, while available at release, are not necessarily noticed or honed until later on because they require a measure of abstract thought and/or an understanding of various other elements and the interplay they create under specific circumstances. In that it takes into account both refined knowledge and practical, creative application, “meta” is kind of that sweet spot between science and art that so many people get drawn to in so many other ways.

Edit: should have read more of these comments before jumping the gun. I dont think I’ve added anything that hasn’t already been said in some way or another. Oops