“Sound whose source is visible on the screen or whose source is implied to be present by the action of the film: voices of characters, sounds made by objects in the story music represented as coming from instruments in the story space ( = source music). Diegetic sound is any sound presented as originated from source within the film’s world Diegetic sound can be either on screen or off screen depending on whatever its source is within the frame or outside the frame. Diegesis is a Greek word for “recounted story”. The film’s diegesis is the total world of the story action.”

Text: Diegetic & Non-Diegetic Sounds. Filmsound.org