Sound

Diegetic sound:

Refers to the world of the text. 

e.g. dialogue, sound effects , music with a source within the text i.e car , bomb.

Non-diegetic sound:

Refers to everything outside the world of the text.

e.g. voiceover , soundtrack, titles, subtitles..

On screen sound:

The audience is can see the source of the sound.

Off-screen sound:

The audience can't see the source of the sound, it also enables the extension of diegetic world.