What does plane polarisation refer to in waves?

Plane polarisation refers to the orientation of oscillations in a wave such that they occur in a single plane. This phenomenon is most commonly observed in light waves, which can oscillate in various directions. However, when light is polarised, the oscillations are restricted to oscillating only along one specific direction, or plane.

In practical applications, such as the use of polarising filters in sunglasses or photography, this characteristic is utilized to reduce glare by eliminating light waves that oscillate in unwanted planes. This selective filtering enhances visibility and contrast in various environments by allowing only the desired orientation of light to pass through.

The other possibilities involve oscillations that are not confined to a single plane—such as oscillations occurring in multiple planes, in all directions, or without any plane constraints— which do not accurately describe the essence of plane polarisation.