Sound terminology

Diegetic sound:

A sound which is made by something shown on or off screen but has been seen by the audience.

For example: the sound of a fast car.

Non-diegetic sound:

A sound which has not been seen on the screen or is incorporated in the film.

For example:A narrator or sound effects

Synchronous sound:Synchronous sounds are those sounds which are synchronized or matched with what is viewed.

For example: If the film portrays a character playing the piano, the sounds of the piano are projected.

Asynchronous sound:Asynchronous sound effects are not matched with a visible source of the sound on screen, however works with story line.
For example:Sound of an ambulance's siren while the foreground sound and image portrays an arguing couple.

Sound effects:Sound effects or audio effects are artificially created or enhanced sounds, or sound processes used to emphasize artistic.

Sound motif: A sound effect or combination of sound effects that are associated with a particular character, setting, situation or idea through the film. 

Sound bridge: Adding to continuity through sound, by running sound (narration, dialogue or music) from one shot across a cut to another shot to make the action seem uninterrupted.

Voice-over:The term voice-over refers to a production technique where a non-diegetic voice is broadcast live or pre-recorded in radio, television, film, theatre and/or presentation.

Ambient sound:Ambient Sound pertains to the pervading atmosphere of a place.