Define plane polarised light.

Explanation

The direction of vibration of electric field vector lies in the plane of sheet of paper. This is called as plane polarised light. The direction vibration of light and its magnitude remains the same.
eg: (a) The blue color of the sky is a scattered light which is plane polarised light.
(b) In a double refraction, OL and EOL both are PPL at right angles to each other.