The system was specifally created for Chess, but is nowadays used by a variety of other games. It serves as the foundation of the ranking-system currently employed by Riot.
Here's an extremly simply explanation on how it works:
- Two players are matched
- The expected outcome of the match is determined by their current elo
- The winner of the match takes elo from the loser. The amount is dependent on the difference in their rating.
As an example:
- TSM plays vs. EG. The expected winner of that match is TSM, because they have a higher rating.
- TSM wins. Because they were expected to win, they will only recieve a few points from EG.
- EG wins. Because they were expected to lose, they take a big number of points from TSM.
For a more in-depth look, click this link to go to Wikpedia