Bb 7alt, 2nd inversion (G# in the bass)
Also written as Bb7alt/G#.
Notes, from the bass up
G# (bass)BC#F#A#D
The same notes as Bb 7alt (G#, B, C#, F#, A# and D), rearranged so G# is the lowest note. Use it to move between chords with smaller jumps across the keyboard.