Gehenna refers to The Valley of the son of Hinnom which is just outside Jerusalem. A selection of verses showing that the Bible uses the term the fire of Gehenna to indicate total destruction.
Kings of Israel burned their sons in the Valley of the son of Hinnom:
In the Old Testament, Sheol is translated as hell, grave or pit. In some Bible versions it is left untranslated. The Bible tells us that Sheol is the place where dead people go.
Jacob said he would go to Sheol (translated grave in some versions) if anything happened to Benjamin, his favourite son: