1. The plane of the incidence containing the incidence ray, the reflected ray and the normal to the interface as shown in figure 2 and
2. The plane perpendicular to the plane of incidence as shown in fig.

If the electric field is only in the plane of incidence then the wave is called as p polarized and if the electric field is perpendicular to the plane of incidence then the wave is called as s polarized.

                                fig : 2