AbmMaj9 is Ab, Cb, Eb, G and Bb. It keeps every note of and adds the .
AbmMaj9 and both contain the 9th. The difference is the 7th: AbmMaj9 uses , while uses the flat 7th.
Choose between them by the seventh under a held 9th. The minor 3rd remains in both chords.
Also written AbmM9, Abm(maj9) or Ab-Δ9.

How you get to it. The turn that lands on AbmMaj9 is to : the ii and the V of Ab minor, which is where a minor tonic is usually arrived at rather than simply begun on.
Hear it land:→→
Contains AbmMaj9 and adds eleventh and flat thirteenth.
Contains AbmMaj9 and adds eleventh and thirteenth.
The common shapes and the derived voicings come from different places, and both are explained in how this site is built.
Shows each chord the way this style would voice it, and marks which of its alternatives belong to the idiom.