Gehenna
Archimandrite Nikifor’s Biblical Encyclopedia
(from Hebrew: the valley of Hinnom) — the name of a deep and narrow ravine on the south side of Jerusalem, in which, under Ahaz, the idolatrous Jews burned their children in honor of the idol Moloch, to the accompaniment of musical instruments, in order to drown out their pitiful cries (see Topheth) (2 Chron. 28:3; Jer. 7:31). King Josiah, in rooting out idolatry, defiled this place — the city’s refuse, human bones, the corpses of executed criminals, and dead animals began to be thrown into it.
To dispel the stench and protect the city from infection, a fire was kept perpetually burning in this valley (Isa. 66:24; Mark 9:43–48), and for this reason this place afterward came to be called the “valley of eternal fire,” and became a place of horror and abomination for the Israelites. In later times this ravine became a symbol of eternal torment, “where the worm dieth not, and the fire is not quenched” (Mark 9:44). In this sense the word “Gehenna” is constantly used by the Lord, either alone or with the addition “of fire” (Matt. 5:29, 30; 10:28; 13:42 [as given]; Mark 9:43–45; Luke 12:5; Matt. 5:22; 18:9; Mark 9:47; James 3:6).