Gehenna, in Hebrew Hinnom. No hell at all, but a valley near Jerusalem, where Israelites immolated their children to Moloch. In that valley a place named Tophet was situated, where a fire was perpetually preserved for sanitary purposes. The prophet Jeremiah informs us that his countrymen, the Jews, used to sacrifice their children on that spot.
Source: H.P.Blavatsky - The Theosophical Glossary