What is a Four Cord?
In the Jazz Vibraphone book on the Milt Jackson chapter I read on page 33: "Blue notes emphasizing the Four Chord" and "One Chord Dominant 7th, b9 scale leading to Four Chord".
I have no idea what is referred to. Who has an idea?
four chord
I believe it is referring to the chord built on the fourth degree of the scale. So, in the key of C, it would be a chord with F as the root.