Clerestory
The clerestory is the upper part of the main wall of a church or cathedral, rising above the aisle roofs and pierced with windows. Its purpose is to bring daylight into the centre of the building, high above the aisles.
In large Gothic churches the clerestory windows run in a continuous band around the nave and choir. Because they are high, the glass in them is seen from far below and is usually simple in design, large in scale and easy to read, with single figures or large patterns. The windows of the aisles below are the place for more detailed scenes.
The word is pronounced “clear-story”, which is how it was spelled in the Middle Ages.