C Minor 7th
m7
0 - 3 - 7 - 10Minor + minor 7th
About C Minor 7th
C minor seventh is a movable four-note chord with no open-string version at all: its notes C, E♭, G and B♭ include two flats the guitar does not offer. What it does offer is a shape that works anywhere on the neck, and that portability is why the chord is learned as a pattern rather than as a position.
The notes
C, E♭, G, B♭. The E♭ makes it minor, the B♭ makes it a seventh, and together they place the chord in the flat keys where guitars rarely start.
The same four notes read from E♭ give E♭6. That equivalence is used constantly in arrangement: a bass moving from C to E♭ under a held chord changes its name without changing a note.
Two positions
Third fret with the root on the A string, or eighth fret with the root on the low E. Both are barres; both are the standard movable minor seventh shapes every guitarist eventually learns.
A partial version on the top four strings drops the root entirely and lets the bass supply it. In a band that is the most common way the chord is actually played.
The absence of an open version has one advantage worth naming: the chord sounds identical in every key, because nothing about it depends on the tuning. Open-string chords each have their own colour; movable ones are uniform, and arrangers rely on that.
Where it shows up
As the ii of B♭ major — the opening chord of a ii–V–I in the key jazz uses most — and as the vi of E♭.
It also appears in soul and gospel as a tonic that never resolves: a vamp on Cm7 with a melody above it can run for a whole verse, because the seventh keeps the chord from sounding final.