guitar chord
A♭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.
Every fingering that fits a hand
444546
moderate · barre
xbbbbb
moderate · barre · no 3
444646
moderate · barre · no 3
464646
hard · barre · no 3
xbbbbx
moderate · barre · no 3, 5
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.
The easiest of the 5 fingerings below is 444546: 3 fingers, one of them barring the 4th fret, held at the 4th fret.
None of them uses an open string, so this chord moves up the neck unchanged — the same shape 1 fret higher is the chord a semitone above.
Where its notes are on the neck
The brass dots are A♭, the root. Everything else is a chord tone with its degree printed in it.
With a different note underneath
A♭11/C
898899
A♭11/E♭
bbbbbb
A♭11/G♭
234322
An inversion is the same chord with a different note lowest. The name changes to a slash name because the bass is what a listener hears as the foundation.