The lake of fire has a meaning similar to that of "the fiery Gehenna [hell fire, King James Version]" that Jesus spoke of. (Matthew 5:22; Mark 9:47, 48)
Gehenna occurs 12 times in the Christian Greek Scriptures, and it refers to the valley of Hinnom, outside the walls of Jerusalem.
When Jesus was on earth, this valley was used as a garbage dump, "where the dead bodies of criminals, and the carcasses of animals, and every other kind of filth was cast." (Smith’s Dictionary of the Bible)
The fires were kept burning by adding sulfur to burn up the refuse. Jesus used that valley as a proper symbol of everlasting destruction.
As does Gehenna, the lake of fire symbolizes eternal destruction.
Death and Hades are "hurled into" it in that they will be done away with when mankind is freed from sin and the condemnation of death.
Willful, unrepentant sinners will also have their "portion" in that lake.
(Revelation 21:8)
They too will be annihilated forever.
On the other hand, those in God’s memory who are in hell—the common grave of mankind—have a marvelous future.