The D flat minor/major seventh chord is a 4-note chord consisting of the notes Db, Fb, Ab and C.
You can see these notes highlighted in the interactive piano chart below.
The chord itself is often abbreviated as Dbm/ma7.
Chords that are a superset of Dbm/ma7. The chords include more notes but always Db, Fb, Ab and C.
Chords that are a subset of Dbm/ma7. These contain less notes but all of them are included in Dbm/ma7.
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 Dbm/ma7 chord. Feel free to save or share the image as needed.