All games can be described as involving the manipulation of game pieces in a game space. The pieces are defined as all of those things which the players have direct control over; the player’s avatar and weapons in an FPS, the pieces on one side in chess, or the player’s own body and any extensions of it, such as a racket or stick, in a physical game. The game space consists of the place in which the pieces exist and are allowed to move, and all those things within it which are not under the sole, direct control of any player, such as armour and health pickups in an FPS or the ball in any number of physical games.

I'm in no way affiliated with this website but I thought this was an ESReality worthy article.

Source: game-central.org/what-makes-a-competitive-game