piano chord
A♭6
A♭1C3E♭5F6
A major triad with a sixth added. The same four notes as a minor seventh chord a third below.
Written the other way round it is G♯6 — the same twelve keys on a piano, a different piece of notation.
What is true of it
A♭6 is A♭, C, E♭ and F — 1, 3, 5 and 6 counted from A♭.
These are also the notes of Fm7/A♭. Which name is right depends on what is underneath and what came before — the notes alone do not decide.
On an instrument that cannot reach all 4, the 5 goes first, in that order.