iv7 chord: The iv7 chord is similar to the IV7 chord, but it is built on the fourth scale degree of a minor key instead of a major key.
Mediant triad (iii or III): The mediant triad is a three-note chord built on the third scale degree of a major or minor key. It adds color and variety to harmonic progressions.
Subdominant: The subdominant refers to the fourth scale degree in a major or minor key. It provides stability and prepares for resolution to the tonic.