A barn is an agricultural building usually on farms and used for various purposes. In North America, a barn refers to structures that house livestock, including cattle and horses, as well as equipment and fodder, and often grain. As a result, the term barn is often qualified e.g. tobacco barn, dairy barn, cow house, sheep barn, potato barn. In the British Isles, the term barn is restricted mainly to storage structures for unthreshed cereals and fodder, the terms byre or shippon being applied to cow shelters, whereas horses are kept in buildings known as stables. In mainland Europe, however, barns were often part of integrated structures known as byre-dwellings (or housebarns in US literature). In addition, barns may be used for equipment storage, as a covered workplace, and for activities such as threshing.
The word barn comes from the Old English bere, for barley (or grain in general), and aern, for a storage place—thus, a storehouse for barley. The word bere-ern, also spelled bern and bearn, is attested to at least sixty times in homilies and other Old English prose. The related words bere-tun and bere-flor both meant threshing floor. Bere-tun also meant granary; the literal translation of bere-tun is "grain enclosure". While the only literary attestation of bere-hus (also granary) comes from the Dialogi of Gregory the Great, there are four known mentions of bere-tun and two of bere-flor. A Thesaurus of Old English lists bere-ærn and melu-hudern ("meal-store house") as synonyms for barn.
The modern barn largely developed from the three aisled medieval barn, commonly known as tithe barn or monastic barn. This, in turn, originated in a 12th-century building tradition, also applied in halls and ecclesiastical buildings. In the 15th century several thousands of these huge barns were to be found in Western Europe. In the course of time, its construction method was adopted by normal farms and it gradually spread to simpler buildings and other rural areas. As a rule, the aisled barn had large entrance doors and a passage corridor for loaded wagons.