also: だいよんのかべ
expression, noun
fourth wall
The conceptual barrier between a fictional work and its audience; used in discussions of theater, film, and games when characters acknowledge the audience or break the illusion.
このゲームでは、主人公がプレイヤーに話しかけて第四の壁を破る。
In this game, the protagonist breaks the fourth wall by talking directly to the player.
演劇で第四の壁を意識させる演出が増えている。
There are more productions in theater that make the audience aware of the fourth wall.
メタフィクション is a broader term for fiction that self-consciously addresses its own fictional nature, while 第四の壁 specifically refers to the barrier between the story and the audience.
Calque from English 'fourth wall', a term from theater theory referring to the imaginary wall between actors and audience.