Although the Greek word Gehenna is translated "hell" in this and other passages (Matthew 23:33, Mark 9:43, etc.), its literal meaning is Valley of Hinnom (Strong's Concordance Number #G1067).

      The valley of Hinnom is a deep, narrow ravine on the south end of Jerusalem. Anciently, it was in this valley that idolatrous Israelites worshipped the pagan gods Moloch and Baal through the abominable sacrificial practice of burning their own children alive (the Bible call this practice "passing through the fire" - See 2Kings 16:3, 23:10; 2Chronicles 28:3, Jeremiah 7:31).

        After the return of the Jews from captivity, the valley was held in such abhorrence that it was made the place to throw all the dead carcasses and filth of the city, and was frequently the place of public executions. The valley, therefore, became extremely offensive; the sight was terrific; the air polluted with the foul spell of putrefying animal and human flesh; and to preserve it in any manner pure, it was necessary to keep fires continually burning there (also known as using unquenched or unquenchable fire).

       Jesus used the well-known fires in the valley of Hinnom as an analogy of the fire (lake of fire) to be used by God to kill forever (the punishment of the incorrigibly wicked is eternal death, NOT eternal torture!) those who refuse to repent of hatred, anger and other sins.

        Some commentaries have suggested that Judas, after he betrayed Jesus, used a tree near a precipice over the valley of Hinnom from which to hang himself.