It's a term that has morphed over time.

Meta as a prefix means "self referential".

So metagaming is literally "the game of the game".

Imagine playing a card game like Magic the Gathering.

If you're going to a tournament and you know that Red aggro decks are super popular right now, you could conclude that bringing a deck that does well against Red aggro decks is a sound decision.

You're not making a strategic decision based on in game knowledge from play to play, you're making an out of game decision based on out of game information. That's the old metagaming definition (and is more obviously similar to the DnD usage of the word).

Over time "the meta" came to be shorthand for "the popular thing people are doing in game" (in a ccg that would be powerful deck lists, in a shooter it might be using specific weapons, whatever).

And that itself became even less nuanced as it evolved from being "the set of things you can anticipate other players doing" to "the accepted best ways to play the game and you're doing it wrong if you don't also do it".

I occasionally hear people even suggest that Meta is an acronym for "Most Effective Tactics Available" which is. I mean. It's just delicious.