The (usually) religious belief that the world will end (in the Final Judgement sense not the kaboom sense) on a multiple of the thousandth year since the birth of Jesus Christ. Although the exact year is the subject of heated debate between Millennialist groups both secular and religious, most of the hardcore believers think that the thousand year reign of the saints mentioned in Revelations will begin on that date.

The term comes from the Greek word for thousand, Chiliiad.