the.com/fourth wall

means The imaginary barrier separating fictional characters from the audience, which they're normally not supposed to acknowledge exists.

from From theater staging: a standard box set has three solid walls visible to the audience, with the implied 'fourth wall' being the open side where the audience watches. The term dates to 19th-century theatrical realism, when directors wanted actors to behave as if that missing wall were truly there — ignoring the audience entirely. 'Breaking the fourth wall' then became the phrase for violating that illusion, stepping outside the fiction to address viewers directly.