Polarisation – the process of transforming waves in which the vibrations travel in multiple planes, into waves with vibrations which travel on a single plane.
Particles in a transverse wave are not restricted in their oscillation direction on the plane perpendicular to the direction of propagation
A transverse wave is said to be plane polarised when all particles oscillate in the same plane all the time
Longitudinal waves cannot be polarised
An unpolarised transverse wave can be polarised using a polariser (Polaroid filter)