A metagame for any game is the way that the game is played. Knowing the metagame is not just knowing the mechanics of the game, but knowing what to expect your opponent to do. It is the relative frequency of each possible tactic, maneuver, build, etc.
One of the easiest to understand examples of this is with collectible card games like Magic: The Gathering and Hearthstone: Heroes of Warcraft. Knowing the metagame in a collectible card game is knowing what styles of decks you might come up against. For example in Magic if your opponent plays an Island on turn one, are they attempting to lock you down, draw you out, make evasive creatures, or any variety of things blue Magic players can do? You don't know if you don't know the metagame.
In StarCraft, for a more localized example, Protoss should wall off against Zerg, but not against Protoss or Terran. Zerg might 6-pool, and if you don't wall off then your opponent is probably going to beat you. As Protoss continues to wall off and 6-pools continue to be ineffective, Zerg players might stop using that strategy. As Zerg players stop 6-pooling, Protoss players might not wall off as often, making the 6-pool effective again. You have to know the current mindset of other players to make the optimal play. That is the metagame.
The metagame is always evolving for any game, so you have to keep playing or reading about your game to keep up with the current metagame.
"Doing the Eraser trick is very easy, you only need two or more Science Vessels with Irradiate researched. To do the trick, simply have your two Science Vessels irradiate each other, and fly them over or near the units you wish to kill. Since Science Vessels are not biological units, Irradiate has no effect on them; however, Irradiate's splash damage hurts surrounding biological units."
It's not a definition set in stone - but it usually refers to a game published by a major publisher, enjoying a large budget (can be millions of dollars) and a large team working on it over a few years. AAA titles typically also have a lot of publicity.
The term does not say anything about the game quality or sales figure.
Best Answer
A metagame for any game is the way that the game is played. Knowing the metagame is not just knowing the mechanics of the game, but knowing what to expect your opponent to do. It is the relative frequency of each possible tactic, maneuver, build, etc.
One of the easiest to understand examples of this is with collectible card games like Magic: The Gathering and Hearthstone: Heroes of Warcraft. Knowing the metagame in a collectible card game is knowing what styles of decks you might come up against. For example in Magic if your opponent plays an Island on turn one, are they attempting to lock you down, draw you out, make evasive creatures, or any variety of things blue Magic players can do? You don't know if you don't know the metagame.
In StarCraft, for a more localized example, Protoss should wall off against Zerg, but not against Protoss or Terran. Zerg might 6-pool, and if you don't wall off then your opponent is probably going to beat you. As Protoss continues to wall off and 6-pools continue to be ineffective, Zerg players might stop using that strategy. As Zerg players stop 6-pooling, Protoss players might not wall off as often, making the 6-pool effective again. You have to know the current mindset of other players to make the optimal play. That is the metagame.
The metagame is always evolving for any game, so you have to keep playing or reading about your game to keep up with the current metagame.