First, we spent time going over a productive definition of games: "A game is a system in which players engage in an artificial conflict, defined by rules, that results in a quantifiable outcome." - Salen & Zimmerman 2004, p80

This definition is elaborated further here.

Further, it is important to create interesting constraints. We had an extended discussion of the meaning of "mechanic" as it relates to games. A few possible definitions follow: