Final answer:
The term for the upper story string of windows in Gothic churches is 'clerestory'. These windows serve to introduce light and add to the upward movement of the design, which is a significant aspect of Gothic church architecture.
Step-by-step explanation:
In the context of Gothic architecture, the term that refers to the upper story string of windows is clerestory.
The clerestory was a significant development in Gothic churches, functioning to admit light and sometimes fresh air, into the grand interiors. It efficiently utilized the advancements in architectural engineering, such as the flying buttresses, to allow the walls to be pierced by large, decorative windows, thus flooding the sacred space with light and creating an otherworldly atmosphere that would elevate the visitor's gaze and spirit.
One of the crowning achievements in Gothic churches, which is accentuated by the clerestory, is the sheer height and grandeur of their lancet windows, which are often paired with an oculus, that together encourage the eyes to look upward. This upward movement is echoed in the interior by the four-part ribbed groin vaults, soaring columns, and light, open feel created by the decorative tracery and extensive stained glass work, especially noted in the Rayonnant period of Gothic architecture.