Second Coming
The Second Coming (sometimes called the Second Advent or the Parousia) is a Christian and Islamic belief regarding the future (or past) return of Jesus Christ after his ascension to heaven about two thousand years ago. The idea is based on messianic prophecies and is part of most Christian eschatologies.
Millerism
The Millerites were the followers of the teachings of William Miller, who in 1833 first shared publicly his belief that the Second Advent of Jesus Christ would occur in roughly the year 1843–1844. Coming during the Second Great Awakening, his beliefs were taken as predictions, spread widely, and were believed by many, leading to the Great Disappointment.