The phenomenon of restriction of vibrating of light waves in particular plane is called polarization of light and such light is called plane polarized light.

The plane in which polarized light vibrates is called plane of vibration. If the fig ABCD is the plane of vibration.

The plane perpendicular to the plane of vibration is called plane of polarization. In the figure EFGH is the plane of polarization.

Polarisation by reflection:

The light reflected from the transparent medium is partially polarised. If reflecting the angle of incidence changed surface the degree of polarisation of reflected light also changes. At particular angle of the incidence the reflected light is completely plane polarised.
The degree of incidence at which the reflected light become completely plane polarised called angle of polarization (θp).