Drop 2 IV

The Drop 2 IV voicing of Fb7#5 stacks Ab, Ebb, Fb and C from the bottom up: the major 3rd, minor 7th, root and sharp 5th of the chord.

It's one of the Drop 2 voicings: four-note chords in close position with the second note from the top dropped an octave, played over the root. The others for Fb7#5 are Drop 2 I, Drop 2 II and Drop 2 III.