Polarization is the orientation of waves to a particular direction. It can occur when the oscillation is perpendicular to the direction of travel of the wave but not when the oscillation is in the same direction as the wave's movement, so it does not occur in sound waves.
Electromagnetic radiation can be polarized, but in astronomy, much is not. Exceptions are maser radiation, radiation from active galaxies, pulsars, the cosmic microwave background, light scattered by dust, and synchrotron radiation. Observation of polarization is used to detect magnetic fields. For dust, polarization suggests non-spherical grains that are aligned, e.g., by a magnetic field. The polarization may be detected in the absorption of starlight, in which case, a number of stars showing identical polarization suggests it was caused by an interstellar cloud in the foreground rather than from the individual star systems.
Polarization can be linear (e.g., like polarized sunglasses) or circular. The latter rotates either rightward or leftward (according to the right hand rule), termed right-hand circular polarization (or RHCP) or left-hand circular polarization (or LHCP).