The word Millennium is from the Latin words "mille," meaning thousand, and "annum," meaning years. It is not a biblical term, other than it is used by many Christian Theologians to identify the thousand year reign spoken of in Revelation Chapter 20. The Word Millennial is referring to that period of time when God says Satan is bound and the Kingdom of Christ goes forth. For all practical purposes, the words Millennium or Millennial is synonymous with "one thousand years". In Theological circles the 1000 year reign of Christ (rev. 20:4) is spoken of as the "Millennial Reign".

In the secular vocabulary, the millennial or millennium is referring to when ever a new thousand years of recorded history since Christ, passes. As the years 1000 A.D., or 2000 A.D is spoken of as the beginning of a new Millennium.