A basin is a bowl-shaped area that holds or collects water. Your bathroom sink has a basin where water gathers before draining away. A mixing bowl is a basin. Even a valley between mountains can be a basin if it collects rainwater and streams flowing down from the peaks.

The word appears frequently in geography. The Amazon Basin describes the enormous area of land where rainfall and rivers drain into the Amazon River. When rain falls anywhere in that vast region (covering much of South America), it eventually flows into the Amazon. Scientists and geographers use basin to describe these natural collecting areas because they function like giant bowls in Earth's surface.

Ocean basins are the deep areas of the ocean floor between continents, formed millions of years ago when Earth's crust shifted and sank. The Pacific Ocean basin is the largest, covering nearly a third of Earth's surface.

When you hear about a “river basin” or “watershed,” it means all the land area that funnels water into that river system. Understanding basins helps scientists track where water comes from, where it goes, and how rainfall in one area affects rivers and communities downstream.