This is a Greek word, meaning: that which is out of sight, the state or place of the dead. Equivalent to the Hebrew: sheol.
The word hades is mentioned in…
“This is not the ultimate hell (Greek: gehenna) referred to in Matthew 10:28, the same as the “lake of fire” (Revelation 20:15). Hades is another compartment in the pit… where the spirits of the unsaved dead are confined until the day of judgment. They were not set free when Christ freed the spirits of the faithful, but are still there” (Dr. Henry M. Morris, The Defenders Study Bible).
All the dead alike went into Hades (sheol) “In Acts 2:27-31 Peter quotes the Septuagint version of Psalms 16:8-11, plainly for the purpose of proving our Lord’s resurrection from the dead. David was left in the place of the dead, and his body saw corruption. Not so with Christ. According to ancient prophecy (Psalms 30:3) he was recalled to life” (Matthew G. Easton).
In Christ’s parable in Luke 16:23, he said “And being in torments in Hades, he [the rich man] lifted up his eyes and saw Abraham afar off, and Lazarus in his bosom” (NKJV).
“Although the two compartments [of Hades] were impassable and separate from each other, they were within the range of mutual sight and sound. This also reveals that disembodied spirits are somehow still recognizable and capable of inter-communication, even though such phenomena are presently beyond our limited understanding” (Dr. Henry M. Morris, The Defenders Study Bible).
“The keys of hell” (hades) (Rev. 1:18)
“Philosophers and occult religionists are always searching for the keys to life and death, but only Christ has them. ‘Hell’ [in the King James Version of Rev. 1:18] is actually ‘Hades,’ the abode of departed souls…
. When Christ died, His spirit descended into Hades, proclaiming victory to the evil spirits incarcerated there, then returned with the souls of those who had died in faith… The unsaved dead will be delivered up from Hades for judgment at the great white throne (Revelation 20:13)” (Dr. Henry M. Morris, The Defenders Study Bible).