This title is only found in the Book of the Revelation. It would be better translated by the word abyss, a very deep place. It must be carefully distinguished from Hell. It has a king, Satan, called " the angel of the bottomless pit." Though it has a king he is not complete master, for the abyss has a key over which Heaven has power, showing there is not unlimited ingress or egress. Satan will be bound in it for the thousand years of the millennial reign-of our Lord on this earth. It is clear that God can and does restrain as well as allow demon activity. We read:
"And now ye know what withholdeth [hindereth] that He might be revealed in His time. For the mystery of iniquity doth already work: only He who now letteth [hindereth] will let [hinder] until He be taken out of the way. And then shall that Wicked be revealed [Antichrist], whom the Lord shall consume with the spirit of His mouth, and shall destroy with the brightness of His coming (2 Thess. 2:6-86And now ye know what withholdeth that he might be revealed in his time. 7For the mystery of iniquity doth already work: only he who now letteth will let, until he be taken out of the way. 8And then shall that Wicked be revealed, whom the Lord shall consume with the spirit of his mouth, and shall destroy with the brightness of his coming: (2 Thessalonians 2:6‑8)).
That God will allow a terrible eruption of demon power to ascend out of the bottomless pit in the last days is seen in Rev. 9. Its description is couched in very colorful and symbolic language.
In the days when the fifth angel shall sound his trumpet of doom, a falling star (a great dignitary, who apostatizes from truth, and who sells himself to the Devil) will have the key of the bottomless pit given to him "And he opened the bottomless pit; and there arose a smoke out of the pit, as the smoke of a great furnace: and the sun and the air were darkened by reason of the smoke of the pit " (Rev. 9:22And he opened the bottomless pit; and there arose a smoke out of the pit, as the smoke of a great furnace; and the sun and the air were darkened by reason of the smoke of the pit. (Revelation 9:2)).
Out of this smoke came locusts, symbolical of spiritual forces, evil spirits, let loose for their work of malevolence. They were like horses prepared for battle, that is, prepared for powerful concerted action. On their heads were crowns of gold, speaking of previous victories, just as soldiers may have a row of medals. They have faces as of men, showing intelligence, but accompanied by subjection and effeminacy, for they had hair like women. They were ferocious for they have teeth like lions. Breastplates of iron sets forth invulnerability when attacked. They have stings like scorpions, speaking of the form of trial they are capable of inflicting, even the instilling of untruth of such a nature as to produce intolerable anguish of spirit, making life unbearable and leading to utter despair.
This gives us a little idea of what tremendous power Satan controls, as far as he is permitted to do so.