Ab 13sus4, 1st inversion (C# in the bass)
Also written as Ab13sus4/C#.
Notes, from the bass up
C# (bass)D#F#A#E#G#
The same notes as Ab 13sus4 (C#, D#, F#, A#, E# and G#), rearranged so C# is the lowest note. Use it to move between chords with smaller jumps across the keyboard.