A suburb is an area within a metropolitan area that often contains most of the areas economic activity, which may include commercial and mixed-use. It can exist either as part of a larger city/urban area or as a separate political entity. Suburbs are residential areas that exist within a reasonable commuting distance of a larger city. They are lower density areas that separate residential and commercial areas from one another. Suburban areas are defined in contrast to central city or inner city areas. The terms inner suburb and outer suburb are used to differentiate between the higher-density areas in proximity to the city center and the lower-density suburbs on the outskirts of the urban area.

Suburbs are often described 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. They are usually differentiated from inner city areas by a focus on spacious residential areas that are much less densely-populated than the large cities they surround.

In most English-speaking countries, suburban areas are defined in contrast to central city or inner city areas, but in Australian English and South African English, 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.

While suburbs are often associated with the middle classes, in many parts of the developed world, suburbs can be economically distressed areas, inhabited by higher proportions of recent immigrants, and marked by decaying infrastructure, poverty, and social problems.