Where I live, in a small city, the housing is mostly single-family homes with yards. Even the downtown area isn’t very dense.
Then, there’s New York City, which has to be the epitome of “dense”. In Manhattan, the buildings are built cheek-by-jowl, and many buildings are very high. The majority of residents of Manhattan live in multi-story apartment buildings, with elevators and doormen. Here are a couple of views of New York City, showing all the tall buildings, built right next to one another. Dense, indeed!