What / who is Hinnom?
We first find Hinnom in Josh.15:8 and 18:16, where he is mentioned in Joshua's layout of the lands of Judah and Benjamin. In II K. 23:10, we find that righteous King Josiah defiled Topheth in the valley of the children of Hinnom that no man might make his son or his daughter to pass through the fire to Molech. Josiah, in his purification of the land of Judah, violated the idolatrous worship to the idol Molech by tearing down the shrines. Topheth (also spelled Tophet) was a word meaning literally, a place of burning. In II Chron. 28.3, idolatrous King Ahaz burnt incense and his children in the fire there, as did idolatrous King Manasseh in II Chron. 33.6. In Neh. 11.30, we find some settling in Topheth after the restoration of the Jewish captives from Babylon. In Jer. 19.2, 6, Jeremiah prophesied calamity coming upon the idolatrous Jews there, calling it the valley of slaughter, because God was going to slaughter the Jews there, using Nebuchadnezzar, King of Babylon. In Jer. 7.32, Jeremiah prophesied destruction coming upon the idolatrous Jews of his day. This word Hinnom in Greek is Gehenna, and is translated as hell in the King James Version, as well as most other versions. Notice the mention of Topheth, the place of burning, again. Isaiah also spoke of Topheth this way in Isa. 30.33, when he warned the pro-Egypt party among the Jews (i.e., those trusting in Egypt for their salvation from Babylon rather than God) of a fiery judgment coming on them. In Jer. 19.11-14, Jeremiah gave this pronouncement of judgment by Babylon on Jerusalem at the valley of Hinnom. This is then the New Testament Gehenna. Gehenna eventually became a place where the nation would burn its refuse. Today we would call it a landfill / garbage dump.