密集 (mì jí): 집중하다.

During rush hour, the subway trains are very frequent, with one every two minutes, but they are still packed with commuters.

This area is densely populated and housing is tight, so the government is planning to build more high-rise apartments.

In summer, the vegetation in this forest is dense, and sunlight can hardly penetrate, making it seem particularly dark.

Before the exam, the teacher assigned us intensive review tasks; we had to do a set of mock questions almost every day.

The commercial district of this city is densely packed with high-rise buildings; walking on the street, you can hardly see the whole sky when you look up.