There is no single answer to what defines a metropolitan area, as the term can have different meanings depending on the context. Generally, though, a metropolitan area is a densely populated area with a high concentration of people and businesses. These areas often encompass multiple counties or even states.

Some of the most densely populated metropolitan areas in the United States are New York City, Los Angeles, Chicago, and Philadelphia. These areas are home to tens of millions of people and are responsible for a large chunk of the country's economic output. Other large metropolitan areas include Tokyo, Mumbai, and Jakarta.