The word aeon, also spelled eon or æon, means "age", "forever" or "for eternity". It is a Latin transliteration from the koine Greek word (aion), from the archaic (aiwon). In Homer it typically refers to life or lifespan, but by at least Hesiod it could refer to ages or generations. It has a similar meaning to the Sanskrit word kalpa and Hebrew word olam. A cognate Latin word aevum or aeuum (cf. ) for "age" is present in words such as longevity and mediæval.

Although a proposal was made in 1957 to define an aeon to be a unit of time equal to one billion years (1 Ga), the idea was not approved as a unit of scientific measure and is seldom used for a specific period of time.Fact: date=November 2007 Its more common usage is for any long, indefinite, period of time.

Eternity or Age

Bible translation is treatment of the Hebrew word olam and the Greek word aion. These two words have similar meaning, and Young's Literal Translation renders them and their derivatives as “age” or “age-during”. Other English versions most often translate them to indicate eternality, being translated as eternal, everlasting, forever, etc. However, there are notable exceptions to this in all major translations, such as : “…I am with you always, to the end of the age” (NRSV), the word “age” being a translation of aion. Rendering aion to indicate eternality in this verse would result in the contradictory phrase “end of eternity”, so the question arises whether it should ever be so. Proponents of Universal Reconciliation point out that this has significant implications for the problem of hell. Contrast in well-known English translations with its rendering in Young's Literal Translation:

And these shall go away to punishment age-during, but the righteous to life age-during. (YLT)

Then they will go away to eternal punishment, but the righteous to eternal life. (NIV)

These will go away into eternal punishment, but the righteous into eternal life. (NASB)

And these shall go away into everlasting punishment, but the righteous into life eternal. (KJV)

And these will depart into everlasting cutting-off, but the righteous ones into everlasting life. (NWT)

In philosophy and mysticism

Plato used the word aeon to denote the eternal world of ideas, which he conceived was "behind" the perceived world, as demonstrated in his famous allegory of the cave.

Christianity's idea of "eternal life" comes from the word for life, zoe, and a form of aeon, which could mean life in the next aeon, the Kingdom of God, or Heaven, just as much as immortality, as in .

Universal Reconciliation according to Christian doctrine, as found in the Greek New Testament scriptures, uses the word "eon" to mean a long period of time (perhaps 1000 years) and the word "eonian" is used to mean "during a long period of time". The New Testament teaching is that there was a time before the eons and that the eonian period of time is now coming to an end. After each man's mortal life ends, they are judged as worthy of eonian life or eonian punishment. That is, after the period of the eons all punishment will cease and death is overcome and then God becomes the all in each one.