The term "ELO" in the context of ranking and rating systems, particularly in chess, refers to Arpad Elo, a Hungarian-American physics professor.
Arpad Elo developed the Elo rating system in the 1960s as a method for calculating the relative skill levels of players in two-player games.
The basic idea behind the Elo system is that after each game, the winner gains points while the loser loses points.
The number of points exchanged depends on the difference in ratings between the two players and the outcome of the match. A higher-rated player is expected to win against a lower-rated player, so if they win, they gain fewer points than if they were to lose.
Over time, this system has been adapted for various competitive activities beyond chess, such as sports, video games, and other one-on-one contests, providing a standardized way to gauge and compare skill levels in different fields.