Ab 13b9, 1st inversion (B# in the bass)
Also written as Ab13b9/B#.
Notes, from the bass up
B# (bass)D#F#AE#G#
The same notes as Ab 13b9 (B#, D#, F#, A, E# and G#), rearranged so B# is the lowest note. Use it to move between chords with smaller jumps across the keyboard.