What is the meaning of blackout shades?

Blackout shades or blackout curtains were utilized during World War Two by England's citizenry to make it more difficult for the Axis' bombers to target their location. Blackout shades or blackout curtains are made from two or three layers of cloth. Thick black cloth for the outside layer, thick white cloth for the inside or middle layer, and an inside thick layer of your color of choice. Many were just two layers, as there was a war going on. These curtains or shades could act as thermal or sound dampers as well.