Despite its name, the Caspian Sea can be called either a lake or a sea. Kukral refers to it as a lake, as do many scholars. It has historically been considered a sea because of its size and its saline water, but it embodies many characteristics of lakes.

The Caspian Sea is called a lake because it is a completely landlocked body of water with no natural, direct connection to the world's oceans. Geographically, it fits the definition of a lake as a large area of water surrounded by land. However, its massive size (the world's largest inland body of water) and its brackish salinity (about 1.2%) give it sea-like characteristics. The "sea" vs. "lake" debate has significant geopolitical implications; under international law, if it were classified as a sea, its resources would be divided based on the United Nations Convention on the Law of the Sea. As a lake, its wealth of oil and gas is divided by treaties between its five bordering nations: Russia, Kazakhstan, Turkmenistan, Iran, and Azerbaijan. Most scientists and international bodies compromise by calling it a "unique body of water" that technically functions as an endorheic lake.