A suburb is an area within a metropolitan area which often contains most of the area's economic activity, which may include commercial and mixed-use. A suburb can exist either as part of a larger city/urban area or as a separate political entity. The name describes an area that is either more or less densely populated than an inner city. In many metropolitan areas suburbs rise in population during the day and are where most jobs are located; being major commercial and job hubs, many suburbs also exist as separate residential communities within commuting distance of a larger city. Suburbs can have their own political or legal jurisdiction, especially in the United States, but this is not always the case, especially in the United Kingdom, where most suburbs are located within the administrative boundaries of cities. 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 U.S., but it is used in contrast with inner city areas.