Elo rating system

The Elo number is a scoring number that describes the playing strength of chess and game players. The concept has since been adapted for various other sports.

Starting with the Bradley-Terry model - named after R. A. Bradley and M. E. Terry, who presented it in 1952 - which in turn was based on a work by Ernst Zermelo from the 1920s,   Arpad Elo developed an objective rating system for the US Chess Federation USCF in 1960. It was adopted by the world chess federation FIDE at the 1970 congress in Siegen. The World Chess Federation calls its system "FIDE rating system". A rating number is officially called "FIDE rating", but in colloquial language it is mostly simply called "Elo number". Besides the international FIDE rating system, there are also national rating systems with different names. In Germany the national rating system is called DWZ, in Austria (national) Elo numbers are calculated and in Switzerland there is a leading list with leading numbers. These systems evaluate muc h more local tournaments, but also calculate the scoring numbers according to the methods of Arpad Elo with mostly only minor modifications and deviating factors

Source
Wikipedia(de) Elo-Zahl