Ocean basins are large, deep areas of the Earth's surface that are covered by saltwater. They are formed by tectonic processes, such as the movement of the Earth's plates, and can vary in size and depth. The major ocean basins include the Pacific Ocean, Atlantic Ocean, Indian Ocean, Southern Ocean, and Arctic Ocean. These basins contain various features, such as mid-ocean ridges, trenches, and seamounts. Mid-ocean ridges are underwater mountain ranges formed by volcanic activity, while trenches are deep, narrow depressions in the ocean floor. Together, these features play a crucial role in the Earth's geology and marine ecosystems.