Sound

Sound can either be diegetic or non diegetic.
Diegetic - this is sound that we see happening on the screen of the film. Example - people talking, musical instruments/radio we see being played, doors we see being closed.
Non diegetic - sound effects used that aren' actually happening on screen. Example - gun shots - guns wouldn't really be shot, so therefore the sound has to be non diegetic.

There are also on screen or off screen sounds.
On screen - sounds we see happening in front of us.
Off screen - sounds we hear but don't see happening, for example hearing people shouting off screen.