IO games are a type of online multiplayer game that originated in 2015 with the release of Agar.io. The game quickly gained popularity due to its simple gameplay, which involves a player controlling a small avatar that can be moved around a game field using the mouse, and trying to consume smaller objects to grow while avoiding being eaten by larger objects.

Since the release of Agar.io, many other IO games have been developed, with gameplay variations ranging from simple survival games to complex strategy games. The common theme among IO games is that they are designed to be played in a web browser and can be played by anyone with an internet connection, making them easily accessible and widely popular.