What is the difference between Sigma and Pi bond?

Sigma bonds are molded by the axial overlapping of the half-filled atomic orbitals of atoms. Pi bonds are developed by the lateral overlapping of the half-filled atomic orbitals of atoms. In sigma bonds, the overlapping of orbitals can be two hybrid orbitals or one hybrid and one pure orbital or two pure orbitals.

In pi bonds, the overlapping of orbitals is always two pure (i.e., unhybridized) orbitals. Sigma bonds permit free rotation. Pi bonds restrict free rotation. Only sigma bonds are included in the control of geometry in polyatomic molecules.