The term borough can means a self-governing township.
In medieval times, boroughs were settlements with some self-government. Boroughs were particularly common in England, Germany and Scotland. In medieval England, boroughs had also the right to elect members of parliament. (The Borough in Southwark, London is thought to have been the original 'borough' of which all others come from.)
Usually a borough is a single town with its own local government. But in some cities it is a sub-division of the city (e.g. London, New York City, Toronto, 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. At certain times London has had no overall city government and London boroughs were the main unit of local government for Londoners.
In other places, such as Alaska, a borough does not mean a single township, but a whole region - in other words, it is similar to a county. In Australia borough can mean a town and its surrounding area, e.g. the Borough of Queenscliffe. Boroughs exist in United Kingdom, more specifically in England and Northern Ireland, in the Canadian province of Quebec, in several U.S. states, in Israel, and formerly they also existed in New Zealand.
At the end of a word, -borough (or -brough) is found in the name of many towns and cities in England; in southern England it is usually spelt -bury. The suffix -bury is also used in the New England region of the United States, while -burg (or -burgh) is more common in Scotland and the American South and West.