The Last Judgement (a.k.a. Judgement Day) is what Christians and some others believe will happen when the world ends.
Zoroastrianism and the religion of Ancient Egypt both include belief in judgement of the dead, therefore skeptics are likely to believe Christianity copied the mythology from one, or both, of those religions.
Only God knows the day and hour, and no man can know it.  It is unclear whether even Jesus knows it despite being one with god, after all if Jesus is man how can he know it? According to the Anglican Westminster Confession of Faith influential with several Protestant sects reprobate angels will be judged as well as humans. 
The events which are prophesied are stated below:-
- A trumpet will sound to wake the dead who will all rise from their graves in the general resurrection. Jesus will stand at the right hand of God Alternatively, according to Roman Catholics, Jesus will appear in the sky sitting on a cloud with
anglesangels all round him. (Matthew 16:27; 24:30; 25:31).
- Next, angels bring humanity to Jesus for judgement (Matthew 24:31), and good people will help Jesus with his judging (1 Corinthians 6:2). 
- God/Jesus will judge mankind, the righteous will go to Heaven and sinners will go to Hell. Part of belief in the Last Judgement is based on a few Gospel passages and part on the Book of Revelation.
Up to the Middle Ages and beyond the stuff about sitting on clouds etc was accepted as fact and Christian Fundamentalists still take it all literally in the 21st century. In modern times many Christians may not know all the weird mythology and Liberal Christians don't take it all literally.
Note that Jesus said that these events would happen within the lifetimes of at least some of his listeners (Matthew 16.28, Mark 14.62, etc.). Mormons acknowledge this, but also believe that there are three Nephites from that period that are still alive today.