Halloween or Hallowe'en is a tradition celebrated on the night of October 31, most notably by children dressing in costumes and going door-to-door collecting sweets, fruit, and other treats. Apart from this trick-or-treating, there are many other traditional Halloween activities. Some of these include costume parties, watching horror films, engaging in vandalism, going to "haunted" houses, and traditional autumn activities such as hayrides, some of these even "haunted". A more complete coverage of Halloween customs can be found at Halloween traditions.

Halloween originated under a different name as a Pagan festival among the Celts of Ireland and Great Britain with Irish, Scots, Welsh and other immigrants transporting versions of the tradition to North America in the nineteenth century. Most other Western countries have embraced Halloween as a part of American pop culture in the late twentieth century.

Halloween is celebrated in most parts of the Western world, most commonly in the United States, Canada, the UK, Ireland, Peru , and with increasing popularity in Australia and New Zealand. In recent years, Halloween has also been celebrated in parts of Western Europe, such as Belgium, France and Spain.

The term Halloween, and its older rendering Hallowe'en, is shortened from All-hallow-eve, as it is the evening of/before "All Hallows' Day"[1] (also known as "All Saints' Day"). The holiday was a day of religious festivities in various northern European Pagan traditions, until Popes Gregory III and Gregory IV moved the old Christian feast of All Saints Day from May 13 to November 1. In the ninth century, the Church measured the day as starting at sunset, in accordance with the Florentine calendar. Although we now consider All Saints (or Hallows) day to be on the day after Halloween, they were, at that time, considered to be the same day.

In Ireland, the name was All Hallows' Eve (often shortened to Hallow Eve), and though seldom used today, it is still a well-accepted label, albeit somewhat esoteric. The festival is also known as Samhain or Oíche Shamhna to the Irish, Calan Gaeaf to the Welsh, Allantide to the Cornish and Hop-tu-Naa to the Manx. Halloween is also called Pooky Night in some parts of Ireland, presumably named after the púca, a mischievous spirit.

Many European cultural traditions hold that Halloween is one of the liminal times of the year when spirits can make contact with the physical world and when magic is most potent (e.g. Catalan mythology about witches, Irish tales of the Sídhe).

Source: http://en.wikipedia.org