The Second Death
The Bible speaks of two deaths. Let first consider the First Death and then we will consider the Second Death. In death there is a separation. The First Death is when we die physically. Hebrews 9:27: "And as it is appointed unto men once to die, but after this the judgment.” In our first death the physical body goes into the grave, but our spirit goes back to God who gave it. We read in Ecclesiastes 12:7, that when we die physically, "Then the dust will return to the earth as it was, and the spirit will return to God who gave it." This is the first death.
Now the second death is for those who are going to be lost eternally in Hell. Those who are lost in Hell will be eternally separated from God. Being eternally separated from God is the Second Death, since death is a separation. We read in Revelation 21:8, " But the fearful, and unbelieving, and the abominable, and murderers, and whoremongers, and sorcerers, and idolaters, and all liars, shall have their part in the lake which burneth with fire and brimstone: which is the second death."