Millennialism (from millennium, Latin for "thousand years"), or chiliasm in Greek, is a belief held by some Christian denominations that there will be a Golden Age or Paradise on Earth in which "Christ will reign" for 1000 years prior to the final judgment and future eternal state (the "World to Come" of the New Heavens and New Earth). This belief is derived primarily from the Book of Revelation 20:1–6. Millennialism as such is a specific form of Millenarianism.
Among Christians who hold this belief, this is not the "end of the world", but rather the penultimate age, the age just prior to the end of Satan's worldwide system in anticipation of a New Heavens and a New Earth under Jehovah's kingdom reign (Rev. 21:1). Some believe that between the millennium proper and the end of the world there will be a brief period in which a final battle with Satan will take place. After this follows the Last Judgment.
Before Christianity, millennialism was first a doctrine of Zoroastrianism. It held that there were successive thousand-year periods, each of which will end in a cataclysm of heresy and destruction, until the final destruction of evil and of the spirit of evil by a triumphant king of peace at the end of the final millennial age (supposed by some to be the year 2000). "Then Saoshyant makes the creatures again pure, and the resurrection and future existence occur" (Zand-i Vohuman Yasht 3:62).
Various other social and political movements, both religious and secular, have also been linked to millennialist metaphors by scholars.
Read more about Millennialism: Early Church and Premillennialism (chiliasm), Reformation and Beyond, Millennialism, Utopianism, Judaism, Jehovah's Witnesses, Nazism, Theosophy, Social Movements