Sound

Why is sound so important in a film?

Sound is used in films to set atmosphere and tone. It allows viewers to hear how loud/quiet an action is.
Dialogue is the most important sound in a film. Without it, the audience wont be as clear on what' happening in the movie.

Director of star wars, George Lukas quotes 'Sound is 50%'. Without sound you only have half the movie.

Sound is vibrations that travel through the air that can be heard.
Soundscape is a piece of music considered in terms of its component sounds.
Sound Design is the process of specifying, acquiring, manipulating or generating audio elements.
Suspending Disbelief is a willingness to suspend one's critical faculties and believe the unbelievable; sacrifice of realism and logic for the sake of enjoyment.

Sound Terms:
Wild Track: removes and replaces background sound.
Ambient Sound: original footage sound. 
Diegetic: all the sounds on the film set.
Non-diagetic: sound added during production.
Score: orchestrally composed sound.
Voiceover: recording over the original footage (eg.narrative).
Dialogue: speech from more than one person.
Dubbing: add new voices (eg. change of language in movies).
Foley: added sound effects.
Synchronous: music matches image and mood.
Asynchronous: music does not match image and mood.
Sound bridge: links to scene.
Sound motif: sounds related to characters (eg. jaws).