The abyss is identified as the same place that held the "angel of the abyss" mentioned at the fifth trumpet
(Rev 9:11).
It is described as bottomless pit (Rev 9:1), a furnace with lots of smoke
(Rev 9:2), and a prison for fallen angels that is strong enough to hold them and requiring
a key (Rev 9:1; 20:1-3).
Elsewhere in the Bible, the abyss is presented as a place of confinement and punishment for fallen angels who indulged in some
form of gross immoral behavior (Luke 8:26-31;
Matt 8:28-32; Jude 1:6-7).