The underground home of the dead in Greek mythology.
Example:
Always careful not to offend, the angry Senator bellowed, "Who in Hades gave out this information about me?"
Hades is both the land of the dead and the god who rules there. Hades (Pluto) the god is the brother of Zeus (Jupiter) and Poseidon (Neptune), who rule the skies and the seas respectively. His own realm is Hades, the region under the earth, full of mineral wealth and fertility and home of the dead. There he rules with his wife Persephone (Proserpina). Hades has become a polite term for Hell and often appears in its place, as in the sentence "The restaurant became hotter than Hades after the air conditioner broke down."