Definition and background:
The lowered seventh note ( leading tone) in the C major scale. In solfeggio it is called Te, in Germany it is called H (The Germans use the letter B to signify a B-flat). The frequencies of the audible pitches of B-flat are notated below. See also [Eng.] B-Flat; [Fr.] Sibemol; [Ger.] B; [It.] Si bemolle; [Sp.] Si bemol.
For more information on the music term "B-flat" check out these other resources:
Wikipedia - Glossary of Musical Terminology
Virginia Tech Multimedia Music Dictionary
ORB -- Medieval Music Glossary