Pi molecular orbitals are formed by sidewise or lateral overlap of atomic orbitals of two atoms on an axis perpendicular to the formation of sigma bonds.For Example : Overlap of Px-Px along Z axis or Overlap of Py-Py along Z axis result in the formation of Pi bonds.Symmetrical overlapping of lobes result in the formation of pi bonding molecular orbitals whereas unsymmetrical overlapping results in formation of Antibonding Pi molecular orbitals.