Diegetic and Non-Diegetic Sound 
Diegetic Sound: 
Diegetic sound includes the voices of characters, talking and dialogue and even the sound of animals like dogs barking. Diegetic sound can also be sounds of the objects in an area. Diegetic sound can be either on screen or off screen depending on its source, if its inside or outside a frame.

This picture is from the film Hot Fuzz, in which the two main characters are talking, the dialogue is diegetic as well the licking and slurping of the ice cream is diegetic. Ticking noises inside the car or the cars engine is also diegetic. Noise outside the car, like peoples footsteps, people shouting, opening doors, crumpling newspaper, are all diegetic sounds.



Non-Diegetic Sound:
Non-Diegetic Sound is the opposite of Diegetic sound, it isn't actual sound. These include of  narrators commentary, sound effects and music.