Final answer:
The underworld, also known as Hades or Sheol, refers to the realm or place of the dead in different cultures and mythologies.
Step-by-step explanation:
The term "underworld" refers to the realm or place of the dead in different cultures and mythologies. It is a concept that has been shaped by various beliefs and can vary in its descriptions. Synonymous terms for the underworld include "Hades" in Greek mythology and "Sheol" in Hebrew and Christian traditions.