Ab Dominant 11th, 1st inversion (B# in the bass)
Notes, from the bass up
B# (bass)D#F#A#C#G#
The same notes as Ab Dominant 11th (B#, D#, F#, A#, C# and G#), rearranged so B# is the lowest note. Use it to move between chords with smaller jumps across the keyboard.