The rules are the borders and the heart of the game. They only refer to the game and never exist outside of the game. Although the game has rules which are like laws, playing a game is voluntary and cannot be forced on the players. Whoever plays a game, voluntarily binds himself to the rules. Where force is involved, there is no game.
Every game has a goal.
The victory condition or requirement. The strategy needed to win the game. I would like to make clear the difference between the two definitions with an example. In the game Go, the victory condition is to earn the most points. In order to achieve this, a player must win space.