Sound 'n' stuff

-Dialogue- All the words and vocal expressions of the actors.
-Music- The music soundtrack that may be in parts or all of the sequence.
-Effects-  Things you might not notice, in the background, like footsteps or traffic.

Sound effects help create a sense of 'reality' of what is happening- We see a door open, and expect to hear it too.

Diegetic

Sounds which come from the world of the film, any event that is seen on or off screen which has a noise audible to the characters.

Non-Diegetic

Sound which is not from any source within the diegetic (world of the movie), such as music or voice-overs  This is usually used to create or enhance audiences emotional responces.

Parallel - Matches the emotions.

Contrapuntal- Contrasts with the emotions. 

Sound Bridge

Used to link two sequences together and is employed in conjunction with editing to move the action in time or place, or both. 

Can be diegetic or non-diegetic sound.

~JB