The Rapture is an event where believers in Christ Jesus / Yeshua, whether they are dead or alive, are saved from having to experience the impending 7 years of Tribulation about to befall on the planet by joining Jesus and going to Heaven for a period of about 7 years. The allegory is that of a groom (Yeshua) coming for His bride (the Church).
For if we believe that Jesus died and rose again, even so God will bring with Him those who sleep in Jesus.[a]
For this we say to you by the word of the Lord, that we who are alive and remain until the coming of the Lord will by no means precede those who are asleep. For the Lord Himself will descend from heaven with a shout, with the voice of an archangel, and with the trumpet of God. And the dead in Christ will rise first. Then we who are alive and remain shall be caught up together with them in the clouds to meet the Lord in the air. And thus we shall always be with the Lord.
- 1 Thessalonians 4:14-17