A minor seventh chord is a minor triad with a minor seventh on top, the note a whole tone below the octave. Cm7 is spelled C–E♭–G–B♭, and Dm7 (D–F–A–C) uses only the white keys of the piano, which makes it an easy chord to find. Chord symbols include Cm7, Cmin7 and C−7.
Because none of its notes pull strongly towards another chord, the minor seventh sounds relaxed and open-ended rather than sad. In jazz it most often appears as the first chord of a ii–V–I, such as Dm7 in the key of C. All four of its notes belong to the Dorian mode, so it is the natural partner of Dorian melodies: the long D Dorian section of Miles Davis’s “So What” (1959) sits on that sound. Stretched to Dm9 or Dm11, the minor seventh is one of the most common colours in jazz lo-fi keyboard loops.