Do you mean the terms “s” and “p”, where s stands for perpendicular to plane of incidence and p is parallel to plane of incidence? In OptiSystem, the electric field is always polarized either in the X or y directions or a combination of them. Therefore, the light is considered as TE or “s” polarized. You cannot define a parallel polarized beam in OptiSystem, partly because it does not simulate wave optics. However, to give you an idea an azimuth of 0 degrees is x polarized light and an azimuth of 90 degrees is y polarized light, since the x axis is defined as the horizontal axis and the y axis is defined as the vertical axis. There are other possible combinations as well for example 45 degrees would be x and y polarized equally.