Anyway, the original definition I gave was:
"A self-contained system of rules that creates a focused reality."
Which I mostly ripped off of Chris Crawfords art of computer game design book, though super condensed.
Anyway the dispute is mostly over the fact that rules need to be "self-contained" and there needs to be a "focused reality", and in fact what a focused reality is.
These words hit a mark with me when I read them in Crawfords book as it was self-evident to me that games must have all their rules included in the game, to be complete. Even having rules such as "the player makes up rules", is a complete set of rules IMO. It is just the definition of the game world/reality.
As for the "focused reality" part, I see this as meaning a common view of the world/reality that all the players (or just the single player) understands and temporarily lives in when they play the game. They act within the game rules, they are basically having a reality defined from them by the game rules. Which is why I think the the "focused reality" is a good term.
He countered with the fact that no one agrees what a reality is and gave examples as to how it was confusing and, to him, a misleading part of the definition and unnecessary.
Anyway, this went on for a while and Ive decided to add on to the original defintion, that games need to be interactive and for the purpose of entertainment as I couldnt think of anything that could be a game without either. So the current definition stands:
"An interactive, self-contained system of rules that creates a focused reality for the purpose of entertainment."
Any comments on any of this? Possible other additions and changes to it?