Bb 7alt, 1st inversion (D in the bass)
Also written as Bb7alt/D.
Notes, from the bass up
D (bass)G#BC#F#A#
The same notes as Bb 7alt (D, G#, B, C#, F# and A#), rearranged so D is the lowest note. Use it to move between chords with smaller jumps across the keyboard.