Gehenna is a term that appears in the New Testament and refers to the Valley of Hinnom, a ravine outside the walls of Jerusalem where garbage was burned, and it was also the site where child sacrifices to the deity moloch where performed in ancient times.
In Jewish tradition, Gehenna became associated with punishment and the afterlife.

Gehenna was used in the New Testament to refer to the concept of hell. Gehenna is a Greek transliteration of the Hebrew term "Ge Hinnom," which means the Valley of Hinnom.
In the New Testament, Jesus used Gehenna as a metaphor for the final destination of the wicked.
The term was used to describe a place of eternal punishment and suffering, where the wicked would be cast out of the presence of Yahweh.

Matthew 5:22: "....whoever shall say, 'You fool', shall be guilty enough to go into Gehenna."
Matthew 5:29: "....it is better for you that one of the parts of your body perish, than for your whole body to be thrown into Gehenna."
Matthew 5:30: "....better for you that one of the parts of your body perish, than for your whole body to go into Gehenna."
Matthew 10:28: "....rather fear Him who is able to destroy both soul [Greek: ψυχή] and body in Gehenna."
Matthew 18:9: "It is better for you to enter life with one eye, than with two eyes to be thrown into the Gehenna...."
Matthew 23:15: "Woe to you, scribes and Pharisees, hypocrites, because you... make one proselyte...twice as much a child of Gehenna as yourselves."
Matthew 23:33, to the Pharisees: "You serpents, you brood of vipers, how shall you escape the sentence of Gehenna?"
Mark 9:43: "It is better for you to enter life crippled, than having your two hands, to go into Gehenna into the unquenchable fire."
Mark 9:45: "It is better for you to enter life lame, than having your two feet, to be cast into Gehenna."
Mark 9:47: "It is better for you to enter the Kingdom of God with one eye, than having two eyes, to be cast into Gehenna."
Luke 12:5: "....fear the One who, after He has killed has authority to cast into Gehenna; yes, I tell you, fear Him."
James 3:6: "And the tongue is a fire,...and sets on fire the course of our life, and is set on fire by Gehenna."

The name given to Hell in Islam, Jahannam, directly derives from Gehenna. The Quran contains 77 references to the Islamic interpretation of Gehenna.

https://en.m.wikipedia.org/wiki/Valley_of_Hinnom_(Gehenna)