Ab Dominant 11th, 5th inversion (C# in the bass)
Notes, from the bass up
C# (bass)G#B#D#F#A#
The same notes as Ab Dominant 11th (C#, G#, B#, D#, F# and A#), rearranged so C# is the lowest note. Use it to move between chords with smaller jumps across the keyboard.