Halloween is a festivity that is celebrated primarily in the United States on the night of October 31 and refers to the ancient traditions of Celtic and Anglo-Saxon culture. Today is also found in other countries around the world and its characteristics are very different: it goes from costume parades for children to play, running from house to house asking for trick or treating.
The origins.

When in the Middle Ages, Christianity spread into Celtic lands and became the official religion of the majority of the Roman Empire, a series of papal edicts instituted a feast day of the church, All Hallows, to be celebrated on November 1 of each year . Shortly after it was established the feast "twin" of All Hallows, or All Souls' Day, celebrated on the next day. The date was set up beside that of All Hallows to emphasize the idea that the saints can intercede on behalf of the dead. In the meantime, many have also begun to celebrate the eve of All Hallows, or the All Hallows Eve (who would become "Halloween").
In Naples we consider that on November 1, the bodies were pulled out of coffins and "disguised". In Britain were held processions to the cemetery where people poured milk on the graves.

HALLOWEEN..NIGHT OF THE WITCHES?

The legend of Jack' o' Lantern.
The oldest is an old Irish legend, or folk tale of Stingy Jack and the Devil. The story is about a drunkard named Jack who managed subtly to deceive the Devil, forcing him to give up forever to possess his sinful soul.
When the old Jack died, however, the pact with the Devil extorted not allow him to enter Hell, the only place to which it was intended, forcing his soul to eternal wandering into nothingness.
The Devil then tossed him an ember from Hell fire, that would always be lit to help Jack find his way through the dark forever. Jack, sad and alone, a carved turnip (which would later become a tradition in the pumpkin) to hold and carry the glowing ember and have a lantern that the company that light was thrown on his way aimlessly.