C♯m7 (also written D♭m7) is a minor seventh chord made of 4 notes: C♯, E, G♯, B. It sounds soft and mellow, a minor chord with the edge taken off, and you hear it in soul, R&B, jazz and smooth pop, often as the ii chord. It is the i chord of C♯ minor and turns up in 5 other keys.
The library above opens on C♯m7 with 14 shapes up and down the neck, starting with hand-checked ones. Tap a shape to hear it, or play it one string at a time.