Gehenna, gehinnam, or gehinnom (Hebrew: גהנום, גהנם, Greek γεεννα) are words used in Jewish and Christian writings for the place where evil people go in the afterlife (see Hell). The name is derived from a geographical site in Jerusalem known as the Valley of Hinnom, one of the two principal valleys surrounding the Old City. Initially the site where idolatrous Jews sacrificed their children to the god Molech (2 Chr. 28:3, 33:6; Jer. 7:31, 19:2-6), the valley later became the common wasteyard for all the refuse of Jerusalem. Here the dead bodies of animals and of criminals, and rubbish, were cast and, according to legend, consumed by a constant fire. In time it became the image of the place of everlasting destruction in Jewish tradition[1]. However, Jewish tradition suggests the valley had a 'gate' which led down to a molten lake of fire. (Possibly 'The furnace of Yahweh' in Zion to which Isaiah refers 31:9, 30:33). It is unknown whether this 'gate' was an actual geophysical feature within the valley that provided the focus for cultic activity (2 Kings 23:10) or simply a metaphorical identification with the entrance to the underworld that had come to be associated with the valley.

Gehenna is cited in the New Testament and in early Christian writing to represent the final place where the wicked will be punished or destroyed after resurrection. In both Rabbinical Jewish and Christian writing, Gehenna as a destination of the wicked is different from Sheol or Hades, the abode of the dead.

Taken from wikipedia.org