Two players with equal ratings who play against each other are expected to score an equal number of wins.
The difference in the ratings between two players serves as a predictor of the outcome of a match. The Elo system was invented as an improved chess-rating system over the previously used Harkness system, but is also used as a rating system in association football, American football, baseball, basketball, pool, table tennis, various board games and esports, and more recently large language models. It is named after its creator Arpad Elo, a Hungarian-American physics professor.
The Elo rating system is a method for calculating the relative skill levels of players in zero-sum games such as chess. Method for calculating the relative skill levels of players in zero-sum games such as chess Arpad Elo, the inventor of the Elo rating system