The concept is also not there. In the Hebrew the word sheol is used. This literally means “the grave” and is used for death and the dead, exactly as we understand it in a modern secular sense.

Gehenna is one of the words used by Jesus. This is dripping with meaning from the Old Testament, where children were burned alive in sacrifice to other gods and buried in a potters field nearby. It is symbolic of meaningless, pointless, anti-covenantal death, then being anonymously buried and forgotten like garbage, rather than beloved family.

Jesus also uses Hades — literally the Greek underworld — for a parable to a Hellenist audience. The parable is about culpability and the permanence of the consequences of wickedness. Wicked people would not be swayed even by a dead relative appearing and warning them. This is a parable, a literary device, not a sudden declaration that the Hellenist underworld, foreign to Judaism, is physically objectively real.

Jewish scripture is surprisingly consistent about this. Dead means dead. None of the New Testament authors contradict this. The controversy of the time was whether the dead would be resurrected and judged at the end of all things. That mythology began during the Maccabean revolt — which is also when the book of Daniel was written and assembled — and which is a major influence on Jesus and his teaching. In that mythology, dead is still dead, but they will be resurrected and judged. The righteous will be given a retirement plan and eternal life in a new creation, those who are not found righteous will be burned like trash and remain dead and forgotten forever.