Vast expanses refer to large areas of land or sea that are difficult to traverse. The term can be used to describe the seas, OCEANS, and SPACE. Seas are large bodies of salt water, usually located between land masses. OCEANS are even larger bodies of salt water, covering most of the Earth's surface. SPACE is the area beyond the Earth's atmosphere, filled with stars, planets, and other celestial objects. Together, these three vast expanses form a large part of the world we live in.