The B flat minor seventh chord is a 4-note chord consisting of the notes Bb, Db, F and Ab.
You can see these notes highlighted in the interactive piano chart below.
The chord itself is often abbreviated as Bbm7.
Chords that are a superset of Bbm7. The chords include more notes but always Bb, Db, F and Ab.
Chords that are a subset of Bbm7. These contain less notes but all of them are included in Bbm7.
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 Bbm7 chord. Feel free to save or share the image as needed.