Polarizer (Polarizing filter)

Polarizer (Polarizing filter)

A filter that is used in bright outdoor settings to create more contrast and color saturation. Polarizers increase the color saturation of the sky and contrast between the sky and clouds while maintaining the color and brightness of the clouds. Polarizers are also used to reduce reflected sunlight or to cut out reflections when shooting reflective surfaces such as water, glass and windows.

courtesy of Wikipedia