Plasma medium in the presence of a static magnetic field behaves like an anisotropic dielectric. Therefore the rules of electromagnetic wave (EMW) propagation are the same as those of the light waves in crystals. The well-established magnetoionic theory is concerned with the study of wave propagation of an arbitrarily polarized plane wave in a cold anisotropic plasma, where the direction of phase propagation of the wave is at an arbitrary angle to the direction of the static magnetic field. As the wave travels in such a medium, the polarization state continuously changes. However, there are specific normal modes of propagation in which the state of polarization is unaltered. Waves with the left (L wave) or the right (R wave) circular polarization are the normal modes in the case of phase propagation along the static magnetic field. Such a propagation is labeled as longitudinal propagation. Ordinary wave (O wave) and extraordinary wave (X wave) are the normal modes for transverse propagation.