“Metagaming” is simply the act of making gameplay decisions based on information not presented from within the game. The classic tabletop RPG example is players having knowledge of a monster’s stat block and thus making tactical decisions that their characters would arguably have not been savvy enough to make.
In Evolve, this would manifest as a hunter team saying “I know that Kraken is the most popular pick, and therefore we should pick a comp that is especially strong against Kraken in order to maximise our chances of success.”
“The meta” as a noun is the term given to the current layout of of how all these decisions are playing out. In a game as small as Evolve, the meta at its most basic will be something like “hunters X, Y, and Z work well together against everything, but monster Q has the best chance of beating them”. Over time this will evolve into “hunters A and B can actually work really well against monster Q, so maybe we should start counter-picking” and so on the cycle goes.
Given a certain state of the game, the meta will tend to ossify over time into certain picks being far and away the most popular until something like a new character or large rules change comes into play to shake things up. This is most easily seen in Standard format MtG; near the end of each block rotation there are generally a handful of deck archetypes that are left in any competitive scene, but even then there will always be rogues, what you call “breaking the meta”, trying new things with varying levels of success. The more mature and long-lived the meta is, the less likely any of these rogue elements are to be successful unless they are truly brand new (unlikely in a game as small as Evolve).
EDIT: lol wasn’t planning on writing an essay but oops
Game theory is a hobby of mine and I’m bored at work :x