If you see a symbol such as C- this does not relate to a bad school report! The minus sign is often used by jazz musicians to indicate a minor chord, so this would be a chord of C minor.
Once we get into chord progressions and ‘diatonic speak ... Let’s explore this with a couple of examples. First, a jazzy II-V-I in C major would be Dm7-G7-Cmaj7. Then, if we move the ...