This expression occurs only in the book of Revelation and is clearly symbolic. The Bible gives its own explanation and definition of the symbol by stating: “This means the second death, the lake of fire.”​—Re 20:14; 21:8.

The symbolic quality of the lake of fire is further evident from the context of references to it in the book of Revelation. Death is said to be hurled into this lake of fire. (Re 19:20; 20:14) Death obviously cannot be literally burned. Moreover, the Devil, an invisible spirit creature, is thrown into the lake. Being spirit, he cannot be hurt by literal fire.​—Re 20:10; compare Ex 3:2 and Jg 13:20.

Since the lake of fire represents “the second death” and since Revelation 20:14 says that both “death and Hades” are to be cast into it, it is evident that the lake cannot represent the death man  has inherited from Adam (Ro 5:12), nor does it refer to Hades (Sheol). It must, therefore, be symbolic of another kind of death, one that is without reversal, for the record nowhere speaks of the “lake” as giving up those in it, as do Adamic death and Hades (Sheol). (Re 20:13) Thus, those not found written in “the book of life,” unrepentant opposers of God’s sovereignty, are hurled into the lake of fire, meaning eternal destruction, or the second death.​—Re 20:15.

While the foregoing texts make evident the symbolic quality of the lake of fire, it has been used by some persons to support belief in a literal place of fire and torment. Revelation 20:10 has been appealed to, because it speaks of the Devil, the wild beast, and the false prophet as being “tormented day and night forever and ever” in the lake of fire. However, this cannot refer to actual conscious torment. Those thrown into the lake of fire undergo “the second death.” (Re 20:14) In death there is no consciousness and, hence, no feeling of pain or suffering.​—Ec 9:5.

In the Scriptures fiery torment is associated with destruction and death. For example, in the Greek Septuagint translation of the Hebrew Scriptures the word for torment (baʹsa·nos) is several times used with reference to punishment by death. (Eze 3:20; 32:24, 30) Similarly, concerning Babylon the Great, the book of Revelation says, “the kings of the earth . . . will weep and beat themselves in grief over her, when they look at the smoke from the burning of her, while they stand at a distance because of their fear of her torment [Gr., ba·sa·ni·smouʹ].” (Re 18:9, 10) As to the meaning of the torment, an angel later explains: “Thus with a swift pitch will Babylon the great city be hurled down, and she will never be found again.” (Re 18:21) So, fiery torment here is parallel with destruction, and in the case of Babylon the Great, it is everlasting destruction.​—Compare Re 17:16; 18:8, 15-17, 19.

Therefore, those who are ‘tormented forever’ (from Gr., ba·sa·niʹzo) in the lake of fire undergo “second death” from which there is no resurrection. The related Greek word ba·sa·ni·stesʹ is translated ‘jailer’ in Matthew 18:34. (RS, NW, ED; compare vs 30.) Thus those hurled into the lake of fire will be held under restraint, or “jailed,” in death throughout eternity.​—See GEHENNA; TORMENT.