The Millennium is a period of a thousand years which some Christians believe will happen after Armageddon but before the end of the world. Only the saved will still be around during the millenium but then Jesus will rule and the world will become a much better place.
End of the world scares happen continually and most adults are cynical about them. Still, children and more credulous adults can get scared over end of the world threats and in the worst cases this even leads to suicide. 
The last major scare was round the year 2000 though there was a smaller scare in 2008 and minor scares affect small numbers of believers at least once most years. The next major scare is due towards the end of 2012.