The term metagame arose in mathematics as a descriptor for set interaction that governs subset interaction in certain cases. The term passed to military use and then to politics to describe actions or events that may have been originally thought of as outside the bounds of the situation in question, but that in fact play an important role in its outcome. For example, a specific military operation could be thought of as a game, with the political ramifications of that operation on the war in general as the metagame. Similarly, a specific political situation such as the passage of a law might be thought of as a game, with the metagame being the larger picture into which that law fits.
Metagame most likely came from the latin word Meta meaning itself. So Metagame about the game itself. We use it as a broad term to describe strategies about the game that are more/most commonly used.