There are two words in the New Testament which have been translated into the English word hell. The first is Hades which is the temporary abode of the dead and the same as Sheol in the Old Testament. The second is the word Gehenna which was used by Jesus Christ to warn people about the dangers of hell. I believe Gehenna is the final or eternal hell.
In the twelfth chapter of the book of Luke, Jesus was speaking to a multitude and said, “And I say unto you my friends, Be not afraid of them that kill the body, and after that have no more that they can do. But I will forewarn you whom ye shall fear: Fear him, which after he hath killed hath power to cast into hell (Gehenna); yea, I say unto you, Fear him.” Luke 12:4-5. This is the beginning of wisdom, when a person starts to fear God. That person has started on the path to eternal life. In another part of the Gospels Jesus spoke stronger words to warn people about the final hell. “And if thy hand offend thee, cut it off: it is better for thee to enter into life maimed, than having two hands to go into hell (Gehenna), into the fire that never shall be quenched: Where their worm dieth not, and the fire is not quenched. And if thy foot offend thee, cut it off: it is better for thee to enter halt into life, than having two feet to be cast into hell, into the fire that never shall be quenched: Where their worm dieth not, and the fire is not quenched. And if thine eye offend thee, pluck it out: it is better for thee to enter into the kingdom of God with one eye, than having two eyes to be cast into hell fire: Where their worm dieth not, and the fire is not quenched.” Mark 9:43-48. Jesus was speaking in symbolic language. Anyone who actually cuts off his hand or plucks out his eye is mentally sick. I heard about one such person and he was mentally and spiritually confused. A parallel scripture to Jesus’ description of hell is given in the Old Testament in the book of Isaiah. “And it shall come to pass, that from one new moon to another, and from one sabbath to another, shall all flesh come to worship before me, saith the Lord. And they shall go forth, and look upon the carcases of the men that have transgressed against me: for their worm shall not die, neither shall their fire be quenched; and they shall be an abhorring unto all flesh.” Isaiah 66: 23-24.