Hinnom, Valley of means in the bible: It was located south and west Jerusalem. This is where the worshippers of Moloch 2 Chr. idolatrous were seen. 28:3; 33:6; Jer. 7:31, 32:35; also see 2 Kgs. 16:3 and 21:6 were used, respectively, as refuse disposal 2 Kgs. 23:10-14. It was known as Gehenna in the New Testament and was considered to be a symbol of the Place of Torment by the Jews.
(in Bible Dictionary)