Light shafts are a type of architectural feature that allow natural light to enter a building. They are typically constructed by cutting a hole in the roof and then covering it with a transparent material such as glass or plastic. The term 'light shaft' is derived from the fact that the light entering the building is directed downwards, creating a shaft of light. The crossword solution 'RAY' is an appropriate answer for this term, as it refers to the beams of light that are created by the light shaft.