The ELO Rating system is a method used to calculate the relative skill levels of players in two-player games, such as chess. Developed by Arpad Elo, it assigns a numerical value to each player based on their performance against other players. When a player wins, they gain points, while the opponent loses points, allowing for a dynamic ranking system. ELO ratings are updated after each match, reflecting the players' current abilities. The difference in ratings between two players predicts the expected outcome of their match. This system is widely used in various competitive games and sports to assess player strength.