The B minor/major 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 Bm/ma7.
Chords that are a superset of Bm/ma7. The chords include more notes but always B, D, F# and A#.
Chords that are a subset of Bm/ma7. These contain less notes but all of them are included in Bm/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 Bm/ma7 chord. Feel free to save or share the image as needed.