Young Red Haired Girl At Home Behind The Window

Thermal, or Diocletian, windows are large semicircular windows (or niches) which are usually divided into three lights (window compartments) by two vertical mullions. The central compartment is often wider than the two side lights on either side of it.
Fixed window
A window that cannot be opened, whose function is limited to allowing light to enter (Unlike an unfixed window, which can open and close). Clerestory windows are often fixed. Transom windows may be fixed or operable.