Diegetic and Non-Diegetic

Diegetic sound

Diegetic sound is the sound that is visible for example;

• Dialogue
• Sound made by objects 
•   Sound made by props 

Diegetic sound can also been known as "actual sound". Diegetic sound also is identifiable by that yu can either see the sound being made or that that you can identify that the sound originated from the scene or previous scene 

Non-Degetic sound

Non-Diegetic sound is where you cant see/infer where sound is coming from for example;

• Sound track
• Commentary
• SFX

Non-Diegetic sound is often used to add effect to a scene for example set a mood with a backing track.

Non-Diegetic sound can also be known as Commentary sound.

Both of these types of sound can be used to create ambiguity or surprise.