piano chord
A♭11
A♭1C3E♭5G♭♭7B♭9D♭11
Six notes in theory; in practice the third is usually dropped, because the eleventh sits a half step above it.
Written the other way round it is G♯11 — the same twelve keys on a piano, a different piece of notation.
What is true of it
A♭11 is A♭, C, E♭, G♭, B♭ and D♭ — 1, 3, 5, b7, 9 and 11 counted from A♭.
On an instrument that cannot reach all 6, the 3, 5 and 1 go first, in that order.