A transom is a horizontal structural beam or bar that is used to support the weight of a structure above it. It is typically made of wood, metal, or concrete, and is often used in the construction of windows, doors, and roofs. In the case of windows and doors, the transom is located above the main opening and is typically fixed in place, while in roofs, it is used to support the rafters and purlins. Transoms can also be used as decorative elements, and can be found in a variety of architectural styles.