piano chord
A♭dim
A♭1C♭♭3E♭♭♭5
Two minor thirds stacked. The fifth is diminished, so it cannot be dropped without losing the chord.
Written the other way round it is G♯dim — the same twelve keys on a piano, a different piece of notation.
What is true of it
A♭dim is A♭, C♭ and E♭♭ — 1, b3 and b5 counted from A♭.
E♭♭ is a double flat, and it has to be: every letter from A♭ upwards is used once, so the b5 cannot be written any other way.