1. A narrative world.
2. (film theory) The spatio-temporal world depicted in the film. Anything within that world (such as dialogue or a shot of a roadsign used to establish a location) is termed diegetic whereas anything outside it (such as a voiceover or a superimposed caption) is extradiegetic. This distinction is especially associated with diegetic sound: for example, when a record-player is shown to be the source of onscreen music. A diegetic audience is an audience within the depicted world.
3. (narratology) The relation of story events by telling, as opposed to showing (mimesis).