Google's Defenition : Specifically in a proscenium theater, the term fourth wall applies to the imaginary invisible wall at the front of the stage in a theater through which the audience sees the action in the world of the play. In an arena theater, or theater-in-the-round, all four walls are in effect "fourth walls." One also speaks of a fourth wall in fictional realms, in literature, movies, television, radio, comic books, and other forms of entertainment.
en.wikipedia.org/wiki/Breaking_the_fourth_wall

And i mean, like if you have a comic pixel. Could a character talk to you! If i'm making sense?