B♭m9 (also written A♯m9) is a minor ninth chord made of 5 notes: B♭, D♭, F, A♭, C. It sounds lush and smooth, and you hear it in neo-soul, R&B and jazz ballads. It is the i chord of B♭ minor and turns up in 5 other keys.
The library above opens on B♭m9 with 8 shapes up and down the neck. Tap a shape to hear it, or play it one string at a time.