Diegetic/Non-Diegetic

Link-http://filmsound.org/terminology/diegetic.htm

The link above is where i got this information.

Diegetic is a sound coming for a real object such as a radio or a car engine 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. While non-diegetic sounds come from off screen such as;

• narrator's commentary
• sound effects which is added for the dramatic effect
• mood music

Non-diegetic sound is represented as coming from the a source outside story space. 

The distinction between diegetic or non-diegetic sound depends on our understanding of the conventions of film viewing and listening.  We know of that certain sounds are represented as coming from the story world, while others are  represented as coming from outside the space of the story events.  A play with diegetic and non-diegetic conventions can be used to create ambiguity (horror), or to surprise the audience (comedy).