Diegesis in Film
Diegetic: Occurs within the story world. It can be explicitly shown on screen, or implicitly implied or assumed. The diegesis occurs within the story world. (As opposed to explicitly stated events and non-diegetic material which constitute the plot.) See: Difference Between Story and Plot
Diegetic dialogue: Dialogue which is in synch with the image onscreen.
Diegetic narration: This is narration by a character within the story world.
Homodiegetic/Intradiegetic Narration: A form of first person diegetic narration, where the narrator is also a participant in the events. Examples of this include Kevin Spacey in American Beauty and Matthew Broderick in Ferris Bueller's Day off, or Robert Downey Jnr. in Kiss Kiss Bang Bang
Heterodiegetic/Extradiegetic Narration: The other form of diegetic narration. Third person narration where the narrator is part of the story world, but is only observing the events. Example: The circus Master in Charlotte's Webb (the book), or pretty much any frame narrator that you can think of. spiregrain came us with a great example: The cowboy figure in The Big Lebowski who, whilst a character in the same fictional world as Lebowski, has no involvement with the plot and only turns to the camera to give occasional narration.
Diegetic music/sound: Music or sounds that can be heard by the characters in the fictional world, such as the television, radio, or the neighbour's annoying dog. This is often used for comic effect in film and television. eg: The audience will assume that a piece of non-diegetic music is playing, until a character turns off the radio and the music stops. Playing with audience expectations creates suprise, and sometimes a quiet chuckle in the back row. | 
