Rev 20:13 The sea gave up the dead who were in it, and Death and Hades delivered up the dead who were in them. And they were judged, each one according to his works.
14 Then Death and Hades were cast into the lake of fire. This is the second death.
15 And anyone not found written in the Book of Life was cast into the lake of fire.
Hades is the tempral place of the dead. It is emptied at this point and those in it are cast into gahana, the lake of fire, tge eternal destination of those who have rejected Christ for their salvation. This is referred to as the second death. A believer in Christ, will only die once tops, physically, but lives thru erernity. True death is seperation from God. We will, nor can we ever be seperated from Him. The second death seals the eternal seperation between God and unrepentant man. We are written in the Book of life. When we accepted Jesus as LORD, He wrote our name in His book.