Guide Tones I

The Guide Tones I voicing of Abm9 stacks Cb and Gb from the bottom up: the minor 3rd and minor 7th of the chord. It leaves out the root, Ab, for the left hand or the bass player to take.

It's one of the Guide Tones voicings: just the 3rd and 7th, the notes that define each chord, played over the root. The other for Abm9 is Guide Tones II.