Revelation 20:1-2, 14

And then I saw an angel descending from heaven, holding the key of the abyss (the bottomless pit) and a great chain was in his hand. And he overpowered and laid hold of the dragon, that old serpent [of primeval times], who is the devil and Satan, and bound him [securely] for a thousand years (a millennium); [Rev 12:7-9, 12, 15]

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]