Lessenar was a planet located somewhere in the space of the galaxy's Alpha or Beta Quadrants, a class M planet that was the homeworld of the Lessenarian civilization. Lessenar's surface was 50% water and 50% land, made up of six continents.

By the 24th century, this world had been heavily polluted by its own inhabitants. By the year 2368, the population was under one million people. (TNG novel: Sins of Commission)