Drop 2 III

The Drop 2 III voicing of Abm(maj7) stacks Ab, Eb, G and Cb from the bottom up: the root, 5th, major 7th and minor 3rd 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 Abm(maj7) are Drop 2 I, Drop 2 II and Drop 2 IV.