The world’s largest inland sea is the Caspian Sea, which is bordered by five countries: Russia, Kazakhstan, Turkmenistan, Iran, and Azerbaijan. Covering an area of about 371,000 square kilometers (143,000 square miles), it is classified as a lake due to its status as a closed basin. Despite being called a "sea," it contains both saltwater and freshwater and is home to diverse aquatic life, including sturgeon fish known for producing caviar. The Caspian Sea has significant geological, ecological, and economic importance, particularly concerning natural resources and biodiversity.