The B-sharp dominant seventh flat five chord (abbreviated "B#7(b5) chord") is a four-note chord consisting of the notes B♯, D, F♯, and A♯. The chord is formed by lowering the fifth of a B-sharp dominant seventh chord a half step.
B-sharp dominant seventh flat five chord
B♯ D F♯ A♯
1 3 ♭5 ♭7
tetrad (four-note chord)