A few years ago, I played in a few Magic: The Gathering tournaments in the Atlanta area. They were always fun because you could test your best deck against anyone else's, and it wasn't expensive to enter.
In Magic, each card has a different ability, so your goal was to combine about 60 cards (out of the thousands available) into a deck that worked. But that wasn't enough to win a tournament. You had to consider the metagame -- the game inside the game. You had to use a deck that would work well against the popular decks of the time. You had to construct a 15-card sideboard that had specific defenses against certain kinds of decks (Protection from Red, for example).
When it comes to poker, game theory and metagame tactics are pretty closely related. Game theory advocates changing your tactics to create an overall better strategy that will presumably win you more money. The metagame adjustments are simply the implementation of that strategy.
The most obvious example is when using in-game data to tailor your decisions to specific opponents. If someone only goes to showdown 15 percent of the time, it makes sense to bluff at him at every opportunity. Most of the time, he will fold. If someone is overly aggressive, you should respond with aggression when you have an edge. If an opponent is a calling station, do not try to bluff him. When against a very loose player preflop, loosen up your calling standards as well. When a super-tight player raises from early position, go ahead and fold hands like AT suited unless there are other reasons to play.
You want to present your strongest game to each of your opponents. When you bluff, you want to make the bluff look real. A ridiculous overbet often is not a good bluff because it's too obvious. Suspicious overbets always look like bluffs -- and sometimes that's exactly what you want.
Matt Matros wrote a column in Card Player discussing how to apply game theory in a no limit hold 'em situation. Here's the question: if you flop a draw with overcards on a paired board, how do you want to play? Do you want to represent the three of a kind? Do you want to bluff? Do you want to simply play your draw? Ideally, you want to accomplish all of these goals at once while maximizing your expectation.
The components of game theory and metagaming break down into many familiar sub-categories, such as game selection, bluff frequency, changing gears, inflection points, flop texture and value bets.
You can call it whatever you want, but each of these tactics are meant to be weighted together to find an answer to the question, "How should I play good poker?"