The rapture in Thess.

1 Thessalonians 4:15-17

¹⁵ For this we say unto you by the word of the Lord, that we which are alive and remain unto the coming of the Lord shall not prevent them which are asleep.

¹⁶ For the Lord himself shall descend from heaven with a shout, with the voice of the archangel, and with the trump of God: and the dead in Christ shall rise first:

¹⁷ Then we which are alive and remain shall be caught up together with them in the clouds, to meet the Lord in the air: and so shall we ever be with the Lord.

http://www.biblegateway.com/passage/?search=1%20Thessalonians%204:1...

In verse 15 what does it mean by remain?