In film studies

Film studies

Film studies is an academic discipline that deals with various theoretical, historical, and critical approaches to films. It is sometimes subsumed within media studies and is often compared to television studies...

, diegesis

Diegesis

Diegesis is a style of representation in fiction and is:# the world in which the situations and events narrated occur; and# telling, recounting, as opposed to showing, enacting.In diegesis the narrator tells the story...

 refers to the story world, and the events that occur within it. Thus, non-diegesis are things which occur outside the story-world.

A non-diegetic insert is a film technique that combines a shot or a series of shots cut into a sequence, showing objects represented as being outside the space of the narrative. Put more simply, a non-diegetic insert is a scene that is outside the story world which is "inserted" into the story world.

Examples

• Three images shown during the disastrous opening night of the play in The Band Wagon
  The Band Wagon
  The Band Wagon is a 1953 musical comedy film that many critics rank, along with Singin' in the Rain, as the finest of the MGM musicals, although it was only a modest box-office success. It tells the story of an aging musical star who hopes a Broadway play will restart his career...
  
  , as a metaphor to highlight how much of a flop the show is.
• Sky sequences shown in Gus Van Sant
  Gus Van Sant
  Gus Green Van Sant, Jr. is an American director, screenwriter, painter, photographer, musician, and author. He is a two time nominee of the Academy Award for Best Director for his 1997 film Good Will Hunting and his 2008 film Milk, both of which were also nominated for Best Picture, and won the...
  
  's Elephant.
• Most famously in The Great Train Robbery a bandit, either following the character's death or before the narrative began, shot his gun directly at the audience.