The Abyss is the abode of the dead (Rom. 10:7) and the place where evil spirits are imprisoned (Rev. 9:1-11).  It is also the watery deep as found in Psalm 77:16.

It is referenced in Luke 8:31; Romans 10:7; Rev. 9:11; Rev. 11:7; Rev. 17:8; Rev. 20:1; Rev. 20:3

• Luke 8:31, They were imploring Him not to command them to go away into the abyss.
• Rom 10:7, or ‘Who will descend into the abyss?’ (that is, to bring Christ up from the dead).”
• Rev 9:11, They have as king over them, the angel of the abyss; his name in Hebrew is Abaddon, and in the Greek he has the name Apollyon.
• Rev 11:7, When they have finished their testimony, the beast that comes up out of the abyss will make war with them, and overcome them and kill them.
• Rev 17:8, “The beast that you saw was, and is not, and is about to come up out of the abyss and go to destruction. And those who dwell on the earth, whose name has not been written in the book of life from the foundation of the world, will wonder when they see the beast, that he was and is not and will come.”
• Rev 20:1, Then I saw an angel coming down from heaven, holding the key of the abyss and a great chain in his hand.
• Rev 20:3, and he threw him into the abyss, and shut it and sealed it over him, so that he would not deceive the nations any longer, until the thousand years were completed; after these things he must be released for a short time.