The event prophesied in 1 Thessalonians 4:16-18 and 1 Corinthians 15:51-52, where Christ comes down in the clouds and the dead believers that are in heaven are resurrected with their new, glorified bodies and caught up to Jesus in the clouds, and then those true believers with faith alone in the gospel (1 Corinthians 15:1-4) that are alive on earth, their bodies are transformed into their new, glorified bodies and then are caught up together with Jesus in the clouds, and then Jesus takes us all to heaven for 7 years while the Tribulation is happening on the earth.
Hundreds of millions of people will suddenly vanish. A strong delusion will come over the whole world to explain away the rapture, and it will probably be an alien abduction.
Young children and babies that can’t comprehend the gospel yet may even be taken as well.