Magic circle
Also said as The circle of play
The boundary between a game and ordinary life. Inside, rules and goals you would never accept elsewhere are real. Johan Huizinga used the phrase in Homo Ludens (1938), and Rules of Play made it a term of game design.
It explains why players accept being lied to, shot at and bankrupted, and why it hurts when the outside gets in, whether through a cheater, a tilted friend or an unskippable advert.
Say it
“Do not put a purchase pop-up in the middle of a match. Everything on this screen should belong to the game; save the store for the menu, outside the circle.”
Where you’ve seen it
At a poker table, lying about your hand is the game and nobody takes offence. Say the same thing about your wages to the same friend the next morning, and it would be a lie.
Not to be confused with immersion
Immersion is a feeling of being absorbed in a world. The magic circle is an agreement about which rules apply, and you can be inside it during a game of cards with no world at all.