The word 'Halloween' comes from a contracted corruption of All Hallows Eve. November 1, "All Hollows Day" (or "All Saints Day"), is a Catholic day of observance in honor of saints. But, in the 5th century BC, in Celtic Ireland, summer officially ended on October 31. The holiday was called Samhain (must be read like 'sow-en')- the Celtic New year. It's one of the 8 celtic festivals.

One story says that, on that day, the disembodied spirits of all those who had died throughout the preceding year would come back in search of living bodies to possess for the next year. It was believed to be their only hope for the afterlife. The Celts believed all laws of space and time were suspended during this time, allowing the spirit world to intermingle with the living. The Still-Living didn't want to be possessed so in that day they made their homes undesiderable and cold and they tried to be as destrustive as possible in order to frighten away spirits.

The spirit of Halloween is considered 'Jack O'Lantern'. Who was Jack? Why did he become the symbol of this celebration?

Jack was an irish man who was used to drink too much liquor at a local pub on All Hallow's Eve. The more drinks Jack consumed the more his life was slipping away. As the intoxicated Jack stumbled home, the Devil demanded that Jack come to Hell with him because of his evil ways. Jack, who was not too eager to die, convinced the Devil to climb a nearby tree to pluck him an apple. As the Devil climbed the tree, Jack carved a cross in the tree's trunk--preventing the Devil from coming back down. The angry and deceived Devil demanded that Jack release him. But first, the clever Jack wanted to make a pact with the Devil. Jack made the Devil promise that when he died the Devil would not claim his soul. The Devil agreed and Jack set him free. On the following All Hallow's Eve Jack died because of too much drinking, and he was denied entrance into heaven and hell and doomed to walk the earth until Judgement Day with only a turnip housing a burning coal to light his way (hence the name jack's lantern, later changed to jack-o'-lantern).