Welcome to PF, Rojan. Polarization is a situation in which the waveforms of the EM field are similarly oriented. Normal light (or other EM) has random orientation. That's a lousy explanation, but I hope that it will suffice until someone more knowledgeable can take over.
Unpolarized light, and electromagnetic waves are light and are a transverse wave, is typicaly generated from a light source where the atoms and molecules changing energy levels act independently...randomly... light a light bulb or the sun...and the light propagated in a given direction consists of independent wavetrains whose planes of vibration are randomly oriented perpendicurlarly to the direction of propagation...the random orientation of the plane waves produces symmetry about the the direction of propagation.
Radio and radar waves, also electromagnetic waves, are not randomly generated...resulting from a surging dipole charge up and down... and so are not symmetric...we say these kinds of waves are polarized...such waves have preferred ...non symmetric...orientations of the electric and magnetic oscillations relative to the direction of propagation...
But note that in the illustration, the light is completely blocked at one orientation...the image gets black...this tells us the light being projected is polarized since all light is blocked at that orientation.