Fourth wall 

The term signifies the suspension of disbelief used by the audience, who are looking in on the action through the invisible wall. The audience thus pretends that the characters in the story are real "living" beings in their own world, and not merely actors performing on a stage or studio set, or written words on the pages of a book. In order for the fourth wall to remain intact, the actors must also, in effect, pretend that the audience doesn't exist, by staying in character at all times and by not addressing the audience members directly. Most such productions rely on the fourth wall.

The literary technique called breaking the fourth wall is used when the plot of a story calls for some event to take place that shatters the barrier between the fictional world of the story, and the "real world" of the audience watching the story.

Examples of breaking the fourth wall include:

• Bertolt Brecht's alienation, or Verfremdungseffekt which was intended to constantly remind the audience that they were watching a show, with the idea that their response would be more thoughtful.
• Thornton Wilder's stage play Our Town includes the character of the Stage Manager, who stands at the side of the stage and addresses the audience directly. The other characters in the play cannot see or acknowledge the narrator's existence. The play is presented on a bare stage with rudimentary props, such as a balcony scene played on a stepladder.
• In Luigi Pirandello's Six Characters in Search of an Author, the fourth wall isn't even there to be broken down. Some actors are getting ready for rehearsal when six characters whose author has died, leaving them incomplete, enter the room. The director decides to include the characters in the play they are rehearsing and soon all the lines between fiction and reality have disappeared.
• The Pirandello play was parodied in a Goon Show episode entitled "Six Charlies in Search of an Author", in which the characters seize the typewriter from one another to write in miraculous escapes, suddenly appearing weapons and the like. All of the Goon Show plots alternated between honoring the fourth wall and breaking it.
• In many animated cartoons, the cartoon characters will suddenly start talking directly to the audience, or encountering a break or tear in the film that the cartoon is being projected upon, or many other ways to remind the audience that they are watching an animated cartoon. Animation director Tex Avery was a pioneer of breaking the fourth wall, and his cartoons often stated, "In a cartoon, you can do anything!"
• In pantomime, characters frequently address remarks to the audience, and sometimes encourage the audience become directly involved in the unfolding of the story.
• In J. M. Barrie's Peter Pan, Peter Pan encourages the good little children who believe in fairies -- in particular, the people reading the story right there and then -- to help make Tinker Bell[?] better, after she drinks Peter's glass of poisoned milk. (The scene is derived from an audience-participation bit in the original stage version, which has roots in pantomime.)
• The Jack Benny Show on radio and television broke the fourth wall, as did The Ernie Kovacs Show and Burns and Allen.
• One of the first movies to tell a fictional story, The Great Train Robbery (1903), ends with a famous shot of a cowboy firing a gun directly at the audience. Legend says that during initial screenings of the film, this scene panicked many members of the studio audience.
• The Daffy Duck cartoon, Duck Amuck is an elaborate and frantic deconstruction of the fourth wall.
• In the Bob and George comic the author appears in the comic.
• The comic The Ruins of the Fourth Wall (http://fireball20xl.com/rotfw/)