Bb 13sus4, 1st inversion (D# in the bass)
Also written as Bb13sus4/D#.
Notes, from the bass up
D# (bass)E#G#B#GA#
The same notes as Bb 13sus4 (D#, E#, G#, B#, G and A#), rearranged so D# is the lowest note. Use it to move between chords with smaller jumps across the keyboard.