Short answers, pulled from the story.
The word barn comes from two Old English roots: bere, meaning barley or grain in general, and aern, meaning a storage place. Together they meant a storehouse for barley. The form bere-ern, also spelled bern and bearn, appears at least sixty times in Old English homilies and prose.
In North America, a barn houses livestock such as cattle and horses, along with equipment, fodder, and often grain, which is why the term is qualified as a tobacco barn, dairy barn, or sheep barn. In the British Isles and Europe, the term is restricted mainly to storage for unthreshed cereals and fodder, while cow shelters are called byres or shippons and horses are kept in stables.
Many barns in the northern United States are painted red with white trim, likely because ferric oxide, used to make red paint, was the cheapest and most readily available chemical for farmers in New England and nearby areas. Ferric oxide may also act as a preservative, helping protect the structure. The custom spread to Scandinavia, where Sweden's Falu red with white trim is traditional for most wooden buildings.
The modern barn largely developed from the three-aisled medieval barn, known as the tithe barn or monastic barn, which originated in a 12th-century building tradition. By the 15th century, several thousand of these huge barns stood across Western Europe. The aisled barn had large entrance doors and a passage corridor for loaded wagons, with storage floors called bays or mows.
The physics term barn is a subatomic unit of area equal to 10 to the minus 28 square metres. It came from experiments with uranium nuclei during World War II, in which the nuclei were described colloquially as big as a barn. The measurement was officially adopted to maintain security around nuclear weapons research.
Barns are classified by function, structure, or location, and include the bank barn, Pennsylvania barn, cantilever barn, combination barn, crib barn, tithe barn, and threshing barn, among others. The tithe barn stored a tenth of the farm's produce owed to the church, while the threshing barn had a threshing floor and large central double doors where grain was beaten by flails and winnowed.