What is Breaking The Fourth Wall manga?

Breaking the fourth wall is the action of addressing or otherwise acknowledging the audience of a work of fiction from within that work, as happens when e.g. the characters of a show speak directly to its viewers. The fourth wall in question is a reference to the imaginary "wall" at the front of the stage of a proscenium theatre, through which the action of the play is seen by the audience; the fourth wall is thus a metaphor for the boundary between what happens inside a fictional work and outside it. This situation is not to be confused with medium awareness, which is when a character shows their awareness of the fact they are a character of a fictional work by e.g. complaining to the writer that they appear in too few episodes.