Millennium

A thousand years; especially, the thousand years mentioned in the twentieth chapter in the twentieth chapter of Revelation, during which holiness is to be triumphant throughout the world. Some believe that, during this period, Christ will reign on earth in person with his saints.

(New Testament) in the Book of Revelation it is foretold that those faithful to Jesus will reign with Jesus over the earth for a thousand years; the meaning of these words have been much debated; some denominations (e.g. Jehovah's Witnesses) expect it to be a thousand years of justice and peace and happiness