In music, an approach chord is a chord one half-step higher or lower than the goal, especially in the context of turnarounds and cycle-of-fourths progressions, for example the two bar 50s progression: |G / Em / |Am / D7 / || may be filled in with approach chords: |G F9 Em Abm |Am D#7 D7 Gb7 || F9 being the half-step to Em, A♭m being the half-step to Am, D♯7 being the half-step to D7, and G♭7 being the half-step to G. G being I, Em being vi, Am being ii, and D7 being V7. Wikipedia