What is game?

What is game? this puzzle me a long time, I'd the feeling i'm not productive when i'm doing games, i feel like i my wasting my time and our customer time. i feel that to continue my path i must understand this definition game.

after some thinking i come out some rough idea

1) game is simplify version of real human or imaginary activities (and therefore, it doesn't inherit the similar risk as the real activities)

2) game is under a structure environment, goal, difficulties and user progress is well defined and measurable

3) game is a system that required human/s interaction to complete. the system has certain challenges to work toward a specified goal. because of it is challenging activities, user rewarding with sense of achievement when the goal is achievement.

and because of this definition, everything could be a game. and everything should be a game :) suddenly i feel like my job is meaningful.