piano chord
G♭11
G♭1B♭3D♭5F♭♭7A♭9C♭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 F♯11 — the same twelve keys on a piano, a different piece of notation.
What is true of it
G♭11 is G♭, B♭, D♭, F♭, A♭ and C♭ — 1, 3, 5, b7, 9 and 11 counted from G♭.
On an instrument that cannot reach all 6, the 3, 5 and 1 go first, in that order.