A suburb is an outlying area within a metropolitan area that has a lower population density than the central city or inner city areas. It is primarily residential and lies outside a citys perimeter. In most English-speaking countries, suburban areas are defined in contrast to central city or inner city areas. However, in Australian English and South African English, the term suburb has become largely synonymous with what is called a "neighborhood" in the US, and the term encompasses inner city areas. In the United Kingdom and Ireland, the term suburb simply refers to a residential area outside the city center, regardless of administrative boundaries. Suburbs can range from areas that seem more like residential areas of a city proper to areas separated by open countryside from the city center. In large cities such as London and Leeds, many suburbs are formerly separate towns and villages that have been absorbed during a citys expansion.

There is no formal definition for what constitutes a suburb in the United States, but it is generally understood to be a smaller community adjacent to or within commuting distance of a city. The term "suburb" usually implies a few characteristics of the built environment, such as sprawling, low-density development, predominantly single-family residential uses, the separation of retail and commercial uses into strip malls, shopping malls, big box stores, and suburban office parks, automobile dependence, and long-distance commutes into the central city for work. However, there is a lack of consensus around the term, and academics are constantly working to establish a scientific definition of the term.