Pit: The Bottomless Pit
Source: Nav
Revelation 9:1, 2, 11
Then the fifth angel sounded his trumpet, and I saw a star that had fallen from heaven to earth, and it was given the key to the pit of the Abyss. / The star opened the pit of the Abyss, and smoke rose out of it like the smoke of a great furnace, and the sun and the air were darkened by the smoke from the pit. / They were ruled by a king, the angel of the Abyss. His name in Hebrew is Abaddon, and in Greek it is Apollyon.
Revelation 11:7
When the two witnesses have finished their testimony, the beast that comes up from the Abyss will wage war with them, and will overpower and kill them.
Revelation 17:8
The beast that you saw—it was, and now is no more, but is about to come up out of the Abyss and go to its destruction. And those who dwell on the earth whose names were not written in the Book of Life from the foundation of the world will marvel when they see the beast that was, and is not, and yet will be.
Revelation 20:1, 3
Then I saw an angel coming down from heaven with the key to the Abyss, holding in his hand a great chain. / And he threw him into the Abyss, shut it, and sealed it over him, so that he could not deceive the nations until the thousand years were complete. After that, he must be released for a brief period of time.