Noun
(music) The major key with B-flat as its tonic, consisting of the pitches B♭, C, D, E♭, F, G, and A.
(music) The major chord with a root of B-flat.
Source: en.wiktionary.orgArnold Schoenberg 's Concerto for String Quartet and Orchestra in B-flat major (1933) was composed after Handel's Concerto Grosso, Op. 6/7. Source: Internet
Clementi also published two symphonies as Op. 18 in 1787, the first in B-flat major and the second in D major. Source: Internet