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