Revelation 20:13-14

And the sea gave up the dead who were in it, and death and Hades (the realm of the dead) surrendered the dead who were in them; and they were judged and sentenced, every one according to their deeds. Then death and Hades [the realm of the dead] were thrown into the lake of fire. This is the second death, the lake of fire [the eternal separation from God]. [Matt 25:41; 1 Cor 15:26]