C 13sus4, 3rd inversion (Bb in the bass)
Also written as C13sus4/Bb.
Notes, from the bass up
Bb (bass)DACFG
The same notes as C 13sus4 (Bb, D, A, C, F and G), rearranged so Bb is the lowest note. Use it to move between chords with smaller jumps across the keyboard.