The A flat eleventh chord is a 5-note chord consisting of the notes Ab, Eb, Gb, Bb and Db.
You can see these notes highlighted in the interactive piano chart below.
The chord itself is often abbreviated as Ab11.
Chords that are a superset of Ab11. The chords include more notes but always Ab, Eb, Gb, Bb and Db.
Chords that are a subset of Ab11. These contain less notes but all of them are included in Ab11.
In case you prefer a non-interactive variant of the chord chart, we've embedded a PNG image below that shows the notes for the the Ab11 chord. Feel free to save or share the image as needed.