What is Elo?
Contrary to popular belief, "ELO" isn't an acronym nor was it invented by Riot. The Elo rating system was made by Arpad Elo, who named the system after himself. It was originally used as (and still is used as) a rating system for chess players, and will most likely use exactly the same algorithm to calculate their skill level, though it will be a close variant if not exactly the same. You can read more about Elo and its creator here upon its Wikipedia article.