Tartarus, or the Abyss. This is a place that is different from Hades, nor is it the lake of fire. "Abyss" signifies deep or bottomless. No human can or will ever go there. It is a temporary holding place for fallen angels. There are at least two groups of fallen angels. There are the angels that fell with Satan in his initial rebellion (Ezek. 28:14-15), and then there are "the angels who sinned" (2 Pet. 2:4) who left "their own original state" (Jude 6), most likely referring to the sons of God (Gen. 6:2). Satan and his demons are free today to roam the earth and the heavenly places (Job 1:6-7), but the group that fell before the flood were cast "down to the deepest pit [Tartarus] of gloom" and are "kept in eternal chains under gloomy darkness". Evidently, Satan and his demons know they will join the others at some "time" in the future; hence they begged Jesus not to send them there early (Luke 8:31; Matt. 8:29). Satan is somehow king of the Abyss, even though he is not banished there yet (Rev. 9:11). When Christ appears, He will cast Satan into the Abyss for 1000 years (Rev. 20:1-3). Satan's demons too will also be cast into the pit for 1000 years, then "visited again" (Isa 24:21-23) when Satan is loosed. The fallen sons of God will never get out until the "great day" of judgment.