Bb Dominant 13th, 6th inversion (G in the bass)
Notes, from the bass up
G (bass)A#DE#G#B#D#
The same notes as Bb Dominant 13th (G, A#, D, E#, G#, B# and D#), rearranged so G is the lowest note. Use it to move between chords with smaller jumps across the keyboard.