Rule
Also said as Game rule
A statement of what is allowed and what happens next: a bishop moves diagonally; touching a ghost costs a life. Rules stay the same however you play.
The fun is in the rules, and one rule can hold up a whole game. Change it and a tense game can turn into a screensaver, with not one pixel of the art different.
Say it
“Add one rule: each apple makes the snake three squares longer. Nothing else changes. That one rule makes the game harder with no new content.”
Where you’ve seen it
Snake rests on one rule: eating makes you longer. Your own tail, the thing you have to avoid, is made out of your success.
Not to be confused with goal
A rule says what can happen. A goal says what you want to happen.