Halloween is a holiday celebrated on the night of October 31. Halloween activities include trick-or-treating, ghost tours, bonfires, costume parties, visiting "haunted houses", carving Jack-o'-lanterns, reading scary stories and watching horror movies. Irish 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 celebrated in several countries of the Western world, most commonly in the United States, Canada, Ireland, Puerto Rico, Japan, New Zealand, United Kingdom and occasionally in parts of Australia.

The term Halloween is shortened from All Hallows' Even as it is the eve of "All Hallows' Day", which is now also known as All Saints' Day. It 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.