piano chord
A♭dim7
A♭1C♭♭3E♭♭♭5G♭♭♭♭7
Three minor thirds stacked. The seventh is doubly diminished, which is why it is written with a double flat.
Written the other way round it is G♯dim7 — the same twelve keys on a piano, a different piece of notation.
What is true of it
A♭dim7 is A♭, C♭, E♭♭ and G♭♭ — 1, b3, b5 and bb7 counted from A♭.
E♭♭ and G♭♭ are double flats, and they have to be: every letter from A♭ upwards is used once, so the b5 cannot be written any other way.