If this is Energy vs Dihedral angle graph of Butane, then I,II and III are respectively :
Fully Eclipsed, Anti, Gauche
I and VII, II and VI, III and V are same.
Energy vs. Dihedral agle or angle of rotation diagram:
Mainly three conformational isomers of butane
Stability order: Staggered > Gauche (Skew) > Eclipsed.
All other infinite possibilities in between staggered and eclipsed conformations are known as skew (Gauche) form.