Hoya Polarization Filter Circular 62mm Black

All light rays reflected by a shiny surface are polarised, which means that the rays that normally oscillate in all directions only oscillate in one direction and cause reflections.
Polarisation filters are used to remove these, which is done by rotating the outer glass relative to the inner, the effect is directly visible through the filter or the camera's viewfinder. It also increases contrast, all this in combination makes it easy for you to get, for example, a blue sky against white clouds or remove unwanted reflections on, for example, a shiny water surface or on windows so you see through them instead of seeing unwanted shine in some cases.

Polarisation filters are usually used as a contrast-absorbing filter in winter landscapes or on other fine days for a more colour-saturated result and to remove unwanted reflections.