Region is defined by a node or focal point, with the surrounding areas linked to that node by transportation systems, communication systems, or other economic associations involving such activities like manufacturing and retail trading

A "functional region" is defined by a "node or focal point", with the near by areas linked to that node by 'transportation systems', 'communication systems', or other 'economic associations' involving the activities like "manufacturing and retail trading".

Explanation:

A region can be called a functional region when there is a routine and regular occurrence of significant activities that involve the exchange of crucial ideas, technological advances, communication, transportation, trade and commerce, manufacturing, etc.