Transom
A transom is a horizontal bar of wood, stone or metal that divides a door or window opening, and by extension the glass panel above it. A transom light sits over a door or between storeys of glazing, and is often fixed so that it cannot open.
In British use a rectangular glass panel over a front door is usually called an overlight or a transom light, and a semicircular one is a fanlight. House numbers are often set in transom glass, in leaded, painted, etched or sandblasted form, so that the number can be seen from the street at night when the hall light is on.
In North America the term transom window is used for both rectangular and arched panels above a door.