Does the lake of fire in Revelation 20 mean eternal conscious torment, annihilation, or something else?

First, eternal damnation is eternal in the sense that those people will never see God. Being deprived of the beatific vision is eternal; if you are sent to hell, forget about it. But there is a remaining question in Catholic theology about conscious torment, and whether that is eternal, and it comes up because it is a matter of justice. We can see that if someone does not love God he will not be in heaven, and he will be punished for his sins. But in normal justice, divine or human, you are punished to the degree of your crime. That is why Jesus and Paul say the punishment in hell will be commensurate with the quantity and quality of your sins, and no more than that. If that is the case, there is a criterion for how you are punished, and there are degrees of punishment in hell. So the other side of that coin says whatever punishment I deserve, to be just, can only last a certain time, because if conscious torment went on for eternity that would be far above the sins I actually committed. There is a question in the church called the sensus poenae, the consciousness of punishment, and the church never says that is eternal; it says your separation from God is eternal. I covered this in my commentary on Matthew and Mark, especially Mark chapter 9, where Jesus speaks of the fire that is not quenched. So there is a possibility that the consciousness of punishment is taken away while you remain eternally damned; and there is a possibility that once you are punished for your sins, having already been eternally separated from God, you are wished out of existence, otherwise called annihilation. The church does not teach annihilation, but the church also does not teach whether that conscious torment is eternal. God is just, and just as he was just in sending you to hell, he will be just in determining your punishment. But the church is the one that makes that decision, so we leave it there. Whenever you see eternal fire or eternal punishment, be careful: eternal means you will never see God for all eternity, but whether it includes the sensus poenae is another question altogether.