eli5 why is the caspian sea considered a sea and not a lake?

Question

I mean it’s completely land locked why isn’t it considered a lake?

In: 2

Answer 1

Because lakes have a drain that ultimately leads to an Ocean. E.g. Lake Superior (one of the largest lakes in the world) drains through several rivers and lakes, which ultimately lead to the Atlantic Ocean.

The Caspian Sea has no such drain, the water doesn’t flow anywhere else. The Caspian Sea mostly loses water through evaporation, which steadily increases its salinity.