Halloween, or Hallowe'en, is a holiday celebrated on the night of October 31. Traditional activities include trick-or-treating, bonfires, costume parties, visiting "haunted houses" and carving jack-o-lanterns. The term Halloween (and its alternative rendering Hallowe'en) is shortened from All-hallow-even, as it is the eve of "All Hallows' Day", also which is now known as All Saints' Day. Some modern Halloween traditions developed out of older pagan traditions, especially surrounding the Irish holiday Samhain, a day associated both with the harvest and otherworldly spirits. Irish and Scottish immigrants carried versions of the tradition to North America in the nineteenth century. Other western countries embraced the holiday in the late twentieth century. Halloween is now celebrated in several parts of the Western world, most commonly in Ireland, the United States, Canada, Puerto Rico, and the United Kingdom and occasionally in parts of Australia and New Zealand.
Many European cultural traditions, in particular Celtic cultures, 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 (according to, for example, Catalan mythology about witches and Scottish and Irish tales of the Sídhe).
Trick-or-treat your asses off!