Cm9 is a minor ninth chord made of 5 notes: C, E♭, G, B♭, D. It sounds lush and smooth, and you hear it in neo-soul, R&B and jazz ballads. It is the i chord of C minor and turns up in 5 other keys.
The library above opens on Cm9 with 14 shapes up and down the neck. Tap a shape to hear it, or play it one string at a time.