The A flat major seventh chord is a 4-note chord consisting of the notes Ab, C, Eb and G.
You can see these notes highlighted in the interactive piano chart below.
The chord itself is often abbreviated as Abmaj7.
Chords that are a superset of Abmaj7. The chords include more notes but always Ab, C, Eb and G.
Chords that are a subset of Abmaj7. These contain less notes but all of them are included in Abmaj7.
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 Abmaj7 chord. Feel free to save or share the image as needed.