Gehenna (Greek γέεννα), Gehinnom (Rabbinical Hebrew: גהנום/גהנם) and Yiddish Gehinnam, are terms derived from a place outside ancient Jerusalem known in the Hebrew Bible as the Valley of the Son of Hinnom (Hebrew: גֵיא בֶן־הִנֹּם or גיא בן-הינום); one of the two principal valleys surrounding the Old City.
In the Hebrew Bible, the site was initially where apostate Israelites and followers of various Ba'als and Caananite gods, including Moloch, sacrificed their children by fire (2 Chr. 28:3, 33:6). Thereafter it was deemed to be cursed (Jer. 7:31, 19:2-6).
In Jewish, Christian and Islamic scripture, Gehenna is a destination of the wicked. This is different from the more neutral Sheol/Hades, the abode of the dead, though the King James version of the Bible translates both with the Anglo-Saxon word Hell.
https://en.wikipedia.org/wiki/Gehenna