ELO

ELO is a rating method, originally from chess, that expresses a player’s skill as a single number. It rises after wins and falls after losses, with larger swings when you beat a much stronger opponent or lose to a weaker one.

Many competitive games use an ELO-style calculation under the hood, even when the visible rank looks different. In everyday use, “ELO” is just shorthand for “skill level.” It is closely related to MMR, which is the in-game implementation of the same idea.