SPACE OF POSSIBILITY:

"The space of possibility of a game is the space of all possible actions and meanings that can emerge in the course of a game. This concept ties together meaning, design, systems, and interactivity... [Interactivity] designers do not directly design play; rather, they only design the structures and contexts in which play takes place, indirectly shaping the actions of the players. We call the space of future action implied by a game design the space of possibility."

Rules of Play, chapter six (pages 67 and 69)