Satellite city

smaller municipality that is adjacent to a major city within a metropolitan area

Satellite cities are smaller cities that are near to a large city that is the center of a metropolitan area. They are different from suburbs, subdivisions and bedroom communities because they have their own center. Satellite cities could be separate cities outside of the larger metropolitan areas. However, working as part of a metropolis, a satellite city gets "cross-commuting" (people living in the city working outside of the city and people from other places working in the city). For example, London has several satellite cities, like Brentwood, Crawley and Chelmsford. New Haven and Bridgeport are among the satellite cities of New York City. Ipswich, Queensland, is a satellite city of Brisbane, Australia, and Kitchener and Guelph are satellite cities of Toronto, Canada.

A metropolitan area usually includes a main city and a series of smaller satellite cities as can be seen in this map of Madrid's metropolitan area (click on the map to enlarge it).
Taoyuan (pictured above; 2.3 million) is the satellite city of Taipei (7 million). Many of the former's residents work in and commute to Taipei.

Satellite cities are almost self sufficient in terms of amenities and facilities. They usually have all of the things to categorize them as a separate city, but they rely on the parent city or the nearby larger metropolitan area for some of their needs like education or employment.