They are usually set in situ and do not open to allow for ventilation. The cost of a standard clerestory window ranges from $1,400 to $2,500. Typical clerestory windows consist of three or more medium-sized windows. They provide light but no view and are used for storage or display purposes. The word "clerestory" comes from Greek kleos (light) and stereon (a building). In Christian churches, the term refers to the gallery above the nave where observers could look down upon the priest and congregation below. The word is also used for similar galleries in other buildings such as theaters and museums. In medieval churches, the word "clerestory" was also used to describe the roofline above the choir, where there might be only one small window or none at all. Today, this area is usually referred to as the gable. As for modern buildings that have a clerestory roof, these are usually found in commercial buildings and factories where they provide light but no view and are used for storage or display purposes.