The E flat eleventh chord is a 5-note chord consisting of the notes Eb, Bb, Db, F and Ab.
You can see these notes highlighted in the interactive piano chart below.
The chord itself is often abbreviated as Eb11.
Chords that are a superset of Eb11. The chords include more notes but always Eb, Bb, Db, F and Ab.
Chords that are a subset of Eb11. These contain less notes but all of them are included in Eb11.
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 Eb11 chord. Feel free to save or share the image as needed.