Definition and background:
The raised sixth note ( submediant) of the C major scale. In solfeggio it is called Li. The frequencies of the audible pitches of A-sharp are notated below. See also [Eng.] A-sharp; [Fr.] La diese; [Ger.] Ais; [It.] La diesis; [Sp.] La sostenido.
For more information on the music term "A-sharp" check out these other resources:
Wikipedia - Glossary of Musical Terminology
Virginia Tech Multimedia Music Dictionary
ORB -- Medieval Music Glossary