Functional region: A region that is made up of different places that are linked and function as a unit.
You are probably familiar with many functional regions. Functional regions are often organized around a central point. A shopping center surrounded by neighborhoods is one example of a functional region. Another example is a large city that is connected to the suburbs by a mass transit system. In some ways, the United States and its associated territories work as a functional unit. The forty-eight contiguous states and Alaska, Hawaii, and the US territories (including Puerto Rico, Guam, and the US Virgin Islands, as well as several others) are scattered over a wide area and have different characteristics. However, since they have political and economic ties, they function as a unit in many ways.