Ab 7b13, 1st inversion (B# in the bass)
Also written as Ab7b13/B#.
Notes, from the bass up
B# (bass)D#F#EG#
The same notes as Ab 7b13 (B#, D#, F#, E and G#), rearranged so B# is the lowest note. Use it to move between chords with smaller jumps across the keyboard.