Matchmaking Rating (MMR) is a secondary rating that is used to match groups of players against others at about the same skill level. Each players MMR increases or decreases with each victory or loss, adjusted by the MMR of the opposing team, and can only be seen at the end of each fight.

Is there MMR in Arena Hearthstone?

Arena does NOT match based on skill / MMR – e.g. if you win a lot at Arena, you dont get stronger opponents when matchmaking. However, “skill level” is also tracked by the devs – this is how they know that, as it turns out, Arena matches are usually decided by skill.