Fourth Wall Meaning

(by extension) The boundary between the fiction and the audience.

Example: 1916, "Second Thoughts on First Nights," New York Times, 20 Feb., p. X7,
  This is a flat, unnecessary, and strangely disturbing denial of the fourth-wall convention, that unwritten agreement between playwright and playgoer whereby you think of yourself at the theatre as a privileged, exonerated, comfortably seated eavesdropper.
2005, Philip Kennicott, "Our Aura of Security, Shattered Like Glass," Washington Post, 31 Aug., p. C01,
  There's been a convention in the theater world to think of the division between audience and spectacle as a fourth wall, a wall that the playwright tries to eliminate through the force of his drama.
1999, Orson Scott Card,
  Even though you, the author, may be maintaining a fourth wall between your characters and your readers, he, the narrator, is not keeping that fourth wall between himself and the audience he thinks he's telling the story to.
2003, Robert Keith Sawyer, Improvised Dialogues: Emergence and Creativity in Conversation, page 107
  The fourth wall is the imaginary barrier between the stage and the audience, and the phrase is a metaphor for the dramatic frame.
2003, Cathy Haase, Acting for Film, page 92
  As actors, we are still looking out into the imaginary fourth wall. The difference is that in film, the fourth wall is no longer fixed;
2004, Diana Fuss, The Sense of an Interior: Four Writers and the Rooms that Shaped Them, page 207
  ... removes the fourth wall of the nineteenth-century novel and, in doing so, eliminates the border between a fictional inside and a nonfictional outside.
2005, Chris Crawford, Chris Crawford on Interactive Storytelling, page 208
  I've saved the worst for last. The crudest scheme is to drop the fourth wall and advise players as to actions that are inhibiting