The Rapture of the church is what is known as the catching away or a carrying away of the church.
"For the Lord Himself will descend from heaven with a shout, with the voice of the archangel, and with the trumpet of God; and the dead in Christ shall 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 will always be with the Lord. Therefore comfort one another with these words."... 1 Thessalonians 4:16-18
The rapture of the church will occur during the church era and is considered by many to happen before the "Great Tribulation" sorrows that befall mankind.
Based on Scripture, there seems to be three different time periods as when the Rapture could take place.
The three possible schools of thought are....
1. Pre-Tribulation Before the seven year Tribulation period.
2. Mid-Tribulation During the middle of the Tribulation period, possibly right before the last 3 1/2 years which are noted as the Great Tribulation period.
3. Post-Tribulation Right after the seven years of Tribulation and during the Second Coming of Jesus Christ