"But I say to you that whoever is angry with his brother without a cause shall be in danger of the judgment. And whoever says to his brother, 'RACA!' shall be in danger of the council. But whoever says, 'YOU FOOL!' shall be in danger of hell fire." (Matthew 5:22, NKJV) Although the Greek word Gehenna is translated "hell" in this and other passages (Matthew 23:33, Mark 9:43, etc.), its literal meaning is the 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). The first mention in the Bible of the valley of Himmon is in the book of Joshua where the borders of the tribe of Judah are defined: "And the border went up by the Valley of the Son of Hinnom to the southern slope of the Jebusite city (which is Jerusalem). The border went up to the top of the mountain that lies before the Valley of Hinnom westward, which is at the end of the Valley of Rephaim northward." (Joshua 15:8, NKJV)
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. Sources: Easton's Bible Dictionary; Albert Barnes' Notes on the Bible; Adam Clark's Commentary on the Entire Bible; Jamieson, Fausset and Brown Commentary | 
