I didn’t pay attention in physics class, why is the light reflected back not polarized? what happened to the once polarized photons that they come back non polarized?

Also what is polarization? I know that Electro Magnetic Radiation or EMR is made up from pulsating magnetic and electrical fields that propagate through space at a fixed rate or frequency… but what does polarization mean? does it mean the fields are slanted to one side or into one direction or something? or is it like some sort of spin or other sort of modulation?