The B minor seventh chord is a 4-note chord consisting of the notes B, D, F# and A.
You can see these notes highlighted in the interactive piano chart below.
The chord itself is often abbreviated as Bm7.
Chords that are a superset of Bm7. The chords include more notes but always B, D, F# and A.
Chords that are a subset of Bm7. These contain less notes but all of them are included in Bm7.
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 Bm7 chord. Feel free to save or share the image as needed.