What do we call a densely populated area containing two or more cities and their surrounding suburbs?

The term "megalopolis" refers to a very large, heavily populated urban area that typically consists of several cities and their surroundings merging into one continuous region. A megalopolis is characterized by its extensive urban sprawl and interconnected infrastructure, allowing for a seamless transition between cities and suburbs. This term is often used to describe regions where multiple metropolitan areas converge, such as the Northeast Corridor in the United States, which includes cities like Boston, New York City, and Washington, D.C.

The concept of a megalopolis captures not just the sheer population density, but also the economic, social, and cultural interconnections that emerge from such large and complex urban environments. Thus, the identification of a densely populated area containing two or more cities and their suburbs as a megalopolis highlights the interconnectedness of multiple urban centers within a larger geographic framework.