What is the meaning of Netherworld?

The place to which one's spirit descends upon death, conceived as below the surface of the earth.

The locale of the spirit world or afterlife, whether deemed to be situated below the world of the living or not.

Specifically, a location of punishment in the afterlife; a hell.

A hidden, shadowy, or sinister subculture, such as that of organized crime.

Source: wiktionary.org