The lake of fire is the eternal prison of the damned. When Satan fell, the lake of fire was "prepared for the devil and his angels" (Matt. 25:41). It was never intended for men, although sadly, the very first occupants will be men. Several names for this place are:
It is called “Gehenna” in Greek, called “Tophet” in Hebrew. Some have asked, how can it be “dark” if it is full of “fire” which produces light? We must understand that these are figures of speech. Fire represents God’s judgment, or torment. A lake has an inlet but no outlet, so it represents a place you can never get out of. Death always means separation, in this case eternal separation from the presence of God (2 Thess. 1:9). Blackness represents solitary confinement. How long will it last?“…fire that never shall be quenched: …where their worm [conscience] dieth not, and the fire is not quenched" (Mark 9:43, 48). What will it be like? “…outer darkness: there shall be the weeping and the gnashing of teeth” (Matt. 8:12). This is the place where the wicked "shall pay the penalty of everlasting destruction" (2 Thess. 1:9).