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… they begged Jesus not to send them there early (Luke 8:31). 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.