The ODP Adult/Games category covers activities that are meant to entertain the participants and that are governed by a specific set of rules. Games are usually competitive, the players are either competing against each other, or against one or more simulated players, or against tasks set by the game rules. There are usually ways to win and lose a game spelled out in the rules.
This category covers sites about nearly any sort of game, including Computer Games, Roleplaying Games, and Gambling Games, and most other activities that refer to themselves as "games". However, Recreation, and Shopping sites belong in separate categories.
Adult/Recreation is for entertaining tasks that may not be competitive, without a way to absolutely win or lose, and not governed by a specific set of rules.
Adult/Shopping is for sites primarily devoted to selling items, including games, but not primarily to describing them or enabling play.