The Rapture and the Disappointed One Left Behind by Dave Hart
The Rapture is an event in the futurist interpretation of Christian eschatology, in which it is posited that Christians will be gathered together in the air to meet Christ at his return. The primary passage used to support this idea is 1 Thessalonians 4:15-17, in which Paul cites "the word of the Lord" about the return of Jesus to gather his saints.

...and the dead in Christ shall rise first: Then we which are alive and remain shall be caught up together with them in the clouds, to meet the Lord in the air.

There are two primary views among Christian denominations regarding the nature of Christ's return:

Dispensationalist Premillennialists (such as many Evangelicals, especially in the United States) hold the return of Christ to be in two stages. 1 Thessalonians 4:15-17 is seen to be a preliminary event to the return described in Matthew 24:29-31. Although both describe a return of Jesus in the clouds with angelic activity, trumpets, heavenly signs, and a gathering of the saints, these are seen to be two separate events. The first event is to be unseen, the rapture proper, when the saved are prophesied to be 'caught up,' from whence the term rapture is taken. The 'second coming' is the public event when Christ's presence is prophesied to be clearly seen as he returns to end Armageddon. The majority of dispensationalists hold that the first event immediately precedes the period of Tribulation. (See chart for additional Dispensationalist timing views);
Amillennialists (such as most Roman Catholics, Eastern Orthodox, Anglicans, Lutherans, Presbyterians (PCUSA), and others), Postmillennialists (such as some Presbyterians, and others), and Historic Premillennialists (such as Calvinistic Baptists, and others) hold that the return of Christ will be a single, public event. All passages regarding the return of Christ, such as Matthew 24:29-31, 1 Thessalonians 4:15-17, 2 Thessalonians 2:1-3, Revelation 1:7, etc., describe the return of Jesus in the clouds amidst trumpets, angelic activity, heavenly signs, a resurrection, and a gathering of saints. Although some (such as some Amillennialists) take this event to be figurative, rather than literal, these three groups maintain that passages regarding the return of Christ describe a single event, and that the "word of the Lord" cited by Paul in 1 Thessalonians 4:15-17 is the Olivet Discourse which Matthew separately describes in Matthew 24:29-31. Although the doctrinal relationship of the rapture and the Second Coming are the same in these three groups, Historic Premillennialists are more likely to use the term "rapture" to clarify their position in distinction from Dispensationalists.