A place is overpopulated when too many people live there for the space, food, water, houses, or jobs that the place can really support. We say it of cities, islands, countries, even of a room that feels packed. It is a judgment about pressure: not just “there are a lot of people,” but “there are more than this place can hold well.” Though actually, “too many” depends on how we live. A dense city with good trains may not feel overpopulated; a small town with no water might. The word is often used in news and school writing about the earth, cities, or animals in a small habitat. It is the adjective; the verb is overpopulate, and the noun is overpopulation. Oddly, the adjective is recorded earlier (1828) than the verb — people named the state before they named the act. Older English had overpeopled and overpopulous for the same idea.