C 7alt, 4th inversion (D# in the bass)
Also written as C7alt/D#.
Notes, from the bass up
D# (bass)AbCEBbDb
The same notes as C 7alt (D#, Ab, C, E, Bb and Db), rearranged so D# is the lowest note. Use it to move between chords with smaller jumps across the keyboard.