What term describes the central, open area typically found in dome structures like the Pantheon?

The term that describes the central, open area typically found in dome structures like the Pantheon is "Oculus." In architectural terms, an oculus refers specifically to a circular opening at the top of a dome, which serves as a source of natural light and ventilation within the space. The oculus of the Pantheon is particularly famous, as it not only illuminates the interior but also creates a connection between the building's interior and the outside environment, allowing light to shift throughout the day.

In contrast, a cupola is a small dome that often crowns a larger dome or building, serving mostly aesthetic purposes or as a lookout point. The term "dome" itself refers broadly to the curved structure that forms the roof, while "pinnacle" typically refers to a pointed formation on top of a building, often seen in Gothic architecture, and does not relate to the central feature of a dome.