What is exactly is antichrist?

In the End times, the antichrist is the individual who during the Great Tribulation, will do his best to bring people down and away from God. The antichrist is part of what's known as the "Unholy Trinity", namely Satan, Antichrist, and the false prophet. All three forces will work together to pull down as many people as possible. Prior to the Great Tribulation, Christ will already have taken out the church, namely those who have trusted him and accepted him as savior. They won't have to face what's coming with the Antichrist. Some people will be saved during the Great Tribulation, but they will be risking their lives by doing so. Those who do become saved will take tremendous risks to bring others to Christ before it's too late for them.