piano chord
A♭9
A♭1C3E♭5G♭♭7B♭9
A dominant seventh carrying a ninth on top.
Written the other way round it is G♯9 — the same twelve keys on a piano, a different piece of notation.
What is true of it
A♭9 is A♭, C, E♭, G♭ and B♭ — 1, 3, 5, b7 and 9 counted from A♭.
On an instrument that cannot reach all 5, the 5 and 1 go first, in that order.