Well, the question is "What is the Metagame?", not "What is your Metagame?"
In which case, the metagame is the overall dominating decks in a certain place or area, which is determined by overall popularity and overall advantage the deck has. If a deck does really well agaisnt several decks in the same place, people will go and start to play that same deck, thus the metagame shifts towards that...
Say for example, that lots of people play ZRE at your league. It's not because everyone had the cards to play ZRE fall in their lap, it's because it's probably the fastest, most dominating deck in that particular area. A deck that that defines the metagame has an advantage agaisnt the other most playable decks in that same area. It defines it, because as I've said, a deck that does good ends up being the deck that everyone plays around there.
Hope this explanation helps.
-Holy Star