The B flat major ninth chord is a 5-note chord consisting of the notes Bb, D, F, A and C.
You can see these notes highlighted in the interactive piano chart below.
The chord itself is often abbreviated as Bbmaj9.
Chords that are a superset of Bbmaj9. The chords include more notes but always Bb, D, F, A and C.
Chords that are a subset of Bbmaj9. These contain less notes but all of them are included in Bbmaj9.
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 Bbmaj9 chord. Feel free to save or share the image as needed.