Rapture is the greatest event of all ages that the church is waiting for. It is the taking away of the true believers in Christ to meet with the lord (1 Thessalonians 4: 16 - 17 ) just as christ was taken up at the end of his first advent.
The rapture is not the same as the second coming of Jesus christ, it is the first phase of he second advent. Christ will appear in the air but will not be visible to the air but will not be visible to the inhabitants of the earth. His mission is to come and resurrect all dead saints, who along with the living believers, who put on immortality and shall be caught up to be with the lord.
the second advent will not take place until after the great tribulation. The time of rapture is unknown, even to the angels (Matthew 24: 36). The rapture will be heralded by the voice of arch angels and blowing of trumpets signalling the end of the church age (1 Thessalonians 4:13 - 18).