Useful Links:

Article on "Symphonic Poem" from Stanley Sadie, ed. The New Grove Dictionary of Music.

Glossary of Film Terms.

"All Movie Guide" Glossary of Film Terms.

Article on "Opera" from Stanley Sadie, ed. The New Grove Dictionary of Opera.
(NOTE: if the above link does not work, you may access this through the Stanford Libraries Website. Enter the Catalogues and Databases menu; click on Databases, then on "N".)

For a glossary of musical terms, consult the Website: www.classicalworks.com/html/glossary.html