»diegetic

The adjective diegetic refers to the source of music in a film: "if [the music] is part of the narrative sphere of the film ... if a character in the film is playing a piano, or turns on a CD, the resulting sound is 'diegetic.' If, on the other hand, music plays in the background but cannot be heard by the film's characters, it is termed non-diegetic or, more accurately, extra-diegetic." I learned the terms "source" and "cue" music some years ago in a film-theory something-or-other, but I prefer this term, which comes from the classical Greek philosophical contrast with mimesis: the contrast of exposition with demonstration.