(Originally Ge bene Hinnom; i.e., "the valley of the sons of Hinnom"), a deep, narrow glen to the south of Jerusalem, where the idolatrous Jews offered their children in sacrifice to Molech (2 Chronicles 28:3; 33:6; Jeremiah 7:31; 19:2-6). This valley afterwards became the common receptacle for all the refuse of the city. Here the dead bodies of animals and of criminals, and all kinds of filth, were cast and consumed by fire kept always burning. It thus in process of time became the image of the place of everlasting destruction. In this sense it is used by our Lord in Matthew 5:22,29,30; 10:28; 18:9; 23:15,33; Mark 9:43,45,47; Luke 12:5. In these passages, and also in James 3:6, the word is uniformly rendered "hell," the Revised Version placing "Gehenna" in the margin. (See HELL; HINNOM .)
These dictionary topics are from M.G. Easton M.A., D.D., Illustrated Bible Dictionary, Third Edition, published by Thomas Nelson, 1897. Public Domain, copy freely.
Easton, Matthew George. "Entry for 'Gehenna'". "Easton's Bible Dictionary".