Annihilation
There are different theories among Christian theologians about the period of punishment in hell. Some people believe hell is a kind of purgatory that cleanses people of their sins before they go to heaven. Others align with annihilationism, in which, after a period, the souls in hell perish into nonexistence. The traditionalists believe that those who are in hell experience torment for eternity.
The annihilationists and the traditionalists differ about the immortality of the human soul. Annihilationists do not believe in the immortality of unrighteous humans. So, they believe that the souls of the impenitent sinners will cease to exist in the lake of fire, or that they will be annihilated forever.
Traditionally, Christians believe that all people, whether saved or lost, will exist eternally because the human soul is immortal. The soul is spiritual and thus has the quality of immortality. And so, the souls of the wicked will suffer in hell eternally.