Polarized light can be identified by light waves aligned parallel to one another. Light is polarized when it is reflected from a transparent material-like glass or when it is scattered by particles suspended in the atmosphere.
Light is a transverse electromagnetic wave, but natural light is generally unpolarized because all planes of propagation are equally probable, as explained by Georgia State University. There are three types of light polarization: linear, circular and elliptical, all of which are composed of two plane waves differing in phase by 90 degrees. The difference between them has to do with the amplification of the individual waves.