The word 'Rapture' does not appear in the bible so, many say this is not a biblical event. This may be so but the event is not dictated to by the appearance of the word. An event which we translate as, Rapture does exist. The Bible term is 'caught up' or 'snatched', and they are in the Bible.
The event is one which will only affect Christians, called in the Bible as 'the called out ones'. The word Christian has been diluted over the years but the Christian that will be snatched will be the one who loves the Lord with all his heart, mind and soul, who follows the will of God and lives his life accordingly.
God has a plan for the world and mankind. It started long ago and the Jews were the chosen race to fulfil that plan, but as we know they did not recognise Jesus as the coming Messiah, prophesied in their scriptures and crucified him. Because of this God turned His attentions to the Gentile nation (the non-Jews) and gave us the gospel, a way to get eternal life. This period of time is called the 'day of grace' or the 'time of the gentiles' and culminates in God removing or 'snatching' the true Christian, out of the earth. Once God has removed the Christian the original plan can be resumed and God will turn once again to the Jew.
Why must he 'snatch' the Christian out? This is because he loves us and part of the plan for the earth is a time of Tribulation, which he does not want us to go through. God works in periods of time and each period does not overlap. One has to finish or be fulfilled before the other starts.
As to the nature of the Rapture it is some times called the Second Coming, which is inaccurate. According to the Bible that is a totally different event. The Rapture is the return of Jesus Christ, but not physically to earth. He only returns as far as the 'clouds in the air' where he waits and 'snatches' or 'seizes up with force' the worthy. No one will see him except those that are called, and they will only see him because they are transformed into a form that is compatible with the Lord himself.
This is why when people speak of the Rapture they say it will be a frightening day for those left because the papers and news will be full of reports of people disappearing in a second, 'in a twinkling of an eye'. We do not exactly know what will happen but other types of rapture in the Bible result in the body disappearing and the soul or the real person goes up to heaven with Christ. This includes those who were dead and those alive, any Christian who meets the requirements as laid down in the Bible.