Ab Major 13th, 1st inversion (B# in the bass)
Notes, from the bass up
B# (bass)D#GA#C#E#G#
The same notes as Ab Major 13th (B#, D#, G, A#, C#, E# and G#), rearranged so B# is the lowest note. Use it to move between chords with smaller jumps across the keyboard.