piano chord
A♭add9
A♭1C3E♭5B♭9
A major triad with a ninth added and no seventh — which is what tells it apart from a ninth chord.
Written the other way round it is G♯add9 — the same twelve keys on a piano, a different piece of notation.
What is true of it
A♭add9 is A♭, C, E♭ and B♭ — 1, 3, 5 and 9 counted from A♭.
On an instrument that cannot reach all 4, the 5 goes first, in that order.