It's the belief that Jesus will have a Second and a Third Coming.
The Second Coming will be in secret. He will be unseen, but all good Christians will suddenly disappear (i.e. He will "rapture" them up into Heaven).
Then comes the tribulation with all its suffering. And then His Third Coming in which the world will end, with the judgment for all.
Rapture Theology is considered a heresy by Catholic, Orthodox, and mainline Protestant churches.
Couldn't care less what the traditional church which has in great part put Jesus to one side consider true or false. I care what God's Word says. The truth is in God's Word not in the traditions of man (Mark 7:7-13).
The Second Coming will be in secret. He will be unseen
It's actually the first part of his second coming (FOR his saints (1 Thess. 4:17)).
Behold, I come as a thief.Revelation 16:15
If therefore you will not watch, I will come on you as a thief, and you shalt not know what hour I will come upon you.Revelation 3:3
But of that day and hour knows no man, no, not the angels of heaven, but my Father only. But as the days of Noah were, so shall also the coming of the Son of man be. For as in the days that were before the flood they were eating and drinking, marrying and giving in marriage, until the day that Noe entered into the ark, and knew not until the flood came, and took them all away; so shall also the coming of the Son of man be. Then shall two be in the field; the one shall be taken, and the other left. Two women shall be grinding at the mill; the one shall be taken, and the other left. Watch therefore: for you do not know what hour your Lord does come.Matt. 24:36-42
etc., etc.
And then His Third Coming in which the world will end, with the judgment for all.
It's actually the second part of his second coming (WITH his saints).
And I saw heaven opened, and behold a white horse; and he that sat upon him was called Faithful and True, and in righteousness he does judge and make war. His eyes were as a flame of fire, and on his head were many crowns; and he had a name written, that no man knew, but he himself. And he was clothed with a vesture dipped in blood: and his name is called The Word of God. And the armies which were in heaven followed him upon white horses, clothed in fine linen, white and clean. And out of his mouth goes a sharp sword, that with it he should smite the nations: and he shall rule them with a rod of iron: and he treads the winepress of the fierceness and wrath of Almighty God. And he has on his vesture and on his thigh a name written, King Of Kings, And Lord Of LordsRevelation 19:11-16,19-21.And I saw the beast, and the kings of the earth, and their armies, gathered together to make war against him that sat on the horse, and against his army and the beast was taken, and with him the false prophet that wrought miracles before him, with which he deceived them that had received the mark of the beast, and them that worshipped his image. These both were cast alive into a lake of fire burning with brimstone. And the remnant were slain with the sword of him that sat upon the horse, which sword proceeded out of his mouth: and all the fowls were filled with their flesh.
Chew on that a while.