1. In narrative theory, the world or story space in which the events of a narrative take place; the story itself as opposed to how it is told.
Usage: literary/academic term; often contrasted with 'mimesis' (showing) and 'discourse' (the manner of telling)
2. In film and media studies, the space and time that exist within the story, as distinct from the space and time of the audience or the presentation itself.
Usage: film/media studies term; diegetic sound or music is sound that exists within the story world

Examples

• In the film, the radio playing in the background is diegetic because it exists within the diegesis.
• The narrator's voice-over commentary exists outside the diegesis and provides external perspective.
• Literary scholars use the term diegesis to describe the internal logic and setting of a fictional world.
• The soundtrack's orchestral score is non-diegetic, while the character's phone ringing is part of the diegesis.
• Understanding the diegesis helps readers distinguish between what happens in the story and how the author presents it.