A borough is an administrative division in various English-speaking countries. In principle, the term borough designates a self-governing walled town, although in practice, official use of the term varies widely.

In the Middle Ages, boroughs were settlements in England that were granted some self-government; burghs were the Scottish equivalent. In medieval England, boroughs were also entitled to elect members of parliament. The use of the word borough probably derives from the burghal system of Alfred the Great. Alfred set up a system of defensive strong points (Burhs); in order to maintain these particular settlements, he granted them a degree of autonomy. After the Norman Conquest, when certain towns were granted self-governance, the concept of the burh/borough seems to have been reused to mean a self-governing settlement.

The concept of the borough has been used repeatedly (and often differently) throughout the world. Often, a borough is a single town with its own local government. However, in some cities it is a subdivision of the city (for example, New York City, London, and Montreal). In such cases, the borough will normally have either limited powers delegated to it by the city's local government, or no powers at all. In other places, such as the U.S. state of Alaska, borough designates a whole region; Alaska's largest borough, the North Slope Borough, is comparable in area to the entire United Kingdom, although its population is less than that of Swanage on England's south coast with around 9,600 inhabitants. In Australia, a borough was once a self-governing small town, but this designation has all but vanished, except for the only remaining borough in the country, which is the Borough of Queenscliffe.

Boroughs as administrative units are to be found in Ireland and the United Kingdom, more specifically in England and Northern Ireland. Boroughs also exist in the Canadian province of Quebec and formerly in Ontario, in some states of the United States, in Israel, formerly in New Zealand and only one left in Australia.

The word borough derives from the Old English word burg, burh, meaning a fortified settlement; the word appears as modern English bury, -brough, Scots burgh, borg in Scandinavian languages, -bert in Dutch and Burg in German.

A number of other European languages have cognate words that were borrowed from the Germanic languages during the Middle Ages, including brog in Irish, bwr or bwrc, meaning "wall, rampart" in Welsh, bourg in French, burg in Catalan (in Catalonia there is a town named Burg), borgo in Italian, burgo in Portuguese, Galician and Castilian (hence the castilian place-name Burgos, galician place-names O Burgo and Malburgo), the -bork of Lębork and Malbork in Polish and the -bor of Maribor in Slovenian.

The 'burg' element, which means "castle" or "fortress", is often confused with 'berg' meaning "hill" or "mountain" (cf. iceberg, inselberg). Hence the 'berg' element in Bergen or Heidelberg relates to a hill, rather than a fort. In some cases, the 'berg' element in place names has converged towards burg/borough; for instance Farnborough, from fernaberga (fern-hill).

A quite distinct word borough, a variant of borgh or borow, was sometimes used historically in south-east England (the county of Kent, and parts of Surrey and Sussex), to mean what was elsewhere called a tithing, a subdivision of a manor or civil parish. The head of such a unit might be known as a headborough. This usage is not to be confused with the more widespread meaning of borough as a privileged town.