m7 Shell

Root + ♭3 + ♭7

Prove it — just do the practice exercise.
Dm7 Shell Voicing
D (R)F (♭3)C (♭7)
In the minor shell, the 3rd changes:

Root
Minor 3rd — one semitone lower than major
Minor 7th — same as Dom7

Example: Dm7 Shell = D + F + C

Mastering 3 shells = ability to comp 80% of jazz standards.