In ancient Greek mythology, Tartarus was a horrible pit of torment in the afterlife. It was lower than even Hades, the place of the dead. According to the Greeks, Tartarus was populated by ferocious monsters and the worst of criminals.
The Greek word Tartarus appears only once in the entire New Testament. Second Peter 2:4 says, “God did not spare angels when they sinned, but sent them to [Tartarus], putting them in chains of darkness to be held for judgment.” Most English versions translate tartarus as “hell” or “lowest hell.” The word Tartarus can be defined as “the deepest abyss of Hades.”
Another place in Scripture that mentions sinning angels is Genesis 6:1–4 where “the sons of God” took control of human women and their progeny. According to Jude 1:6, some angels “abandoned their proper dwelling” in the heavens. For this crime, God cast them into Tartarus where they are held “in pits of gloom” (AMP) for a later judgment. It seems that Tartarus was what the demons feared in Luke 8:31.
Peter’s mention of Tartarus is in the context of condemning false teachers. Those who secretly introduce heresy into the church will suffer a fate similar to that of the angels who sinned—they will end up in Tartarus. The Lord does not tolerate those who lead His children astray (Matthew 18:6).