Transom (architecture)

[1][2] In Britain, the transom light is usually referred to as a fanlight, often with a semi-circular shape, especially when the window is segmented like the slats of a folding hand fan.

[3] Transom windows which could be opened to provide cross-ventilation while maintaining security and privacy (due to their small size and height above floor level) were a common feature of apartments, homes, office buildings, schools, and other buildings before central air conditioning and heating became common beginning in the early-to-mid 20th century.

[8] Similarly, the phrase is used to describe the means by which confidential documents, information or tips were delivered anonymously to someone who is not officially supposed to have them.

"Like pushing a piano through a transom" is a folk idiom used to describe something exceedingly difficult; its application to childbirth (and possibly its origin) has been attributed to Alice Roosevelt Longworth and Fannie Brice.

These details can be anything from simple shōji-style dividers to elaborate wooden carvings, and they serve as a traditional welcome to visitors of the head of the household.