What does Paul mean by "that day"?

The Thessalonians were troubled that they had missed "that day." Then Paul told them that "that day" would not come before the emergence of the Antichrist. What does "that day" refer to? The Rapture? The Second Coming? Are the rapture and the Second Coming simultaneous events, or separate?

Also, what was this false teaching that was being spread?

2 Thessalonians 2:3

AMP - ³ Let no one deceive or beguile you in any way, for that day will not come except the apostasy comes first [unless the predicted great falling away of those who have professed to be Christians has come], and the man of lawlessness (sin) is revealed, who is the son of doom (of perdition).

Clarify • Share • Report • Asked July 12 2013 • Online Buddy