Halloween or Hallowe’en (a contraction of “All Hallows’ evening”),^[5] less commonly known as Allhalloween,^[6] All Hallows’ Eve,^[7] or All Saints’ Eve,^[8] is a celebration observed in many countries on 31 October, the eve of the Western Christian feast of All Hallows’ Day. It begins the observance of Allhallowtide,^[9] the time in the liturgical year dedicated to remembering the dead, including saints (hallows), martyrs, and all the departed.^[10][11]

One theory holds that many Halloween traditions were influenced by Celtic harvest festivals, particularly the Gaelic festival Samhain, which are believed to have pagan roots.^{[12][13][14][15]} Some go further and suggest that Samhain may have been Christianized as All Hallow’s Day, along with its eve, by the early Church.^[16] Other academics believe Halloween began solely as a Christian holiday, being the vigil of All Hallow’s Day.^{[17][18][19][20]} Celebrated in Ireland and Scotland for centuries, Irish and Scottish migrants brought many Halloween customs to North America in the 19th century,^[21][22] and then through American influence, Halloween spread to other countries by the late 20th and early 21st century.^[23][24]

Halloween activities include trick-or-treating (or the related guising and souling), attending Halloween costume parties, carving pumpkins into jack-o’-lanterns, lighting bonfires, apple bobbing, divination games, playing pranks, visiting haunted attractions, telling scary stories, and watching horror or Halloween-themed films.^[25] For some people, the Christian religious observances of All Hallows’ Eve, including attending church services and lighting candles on the graves of the dead, remain popular,^[26][27][28] although it is a secular celebration for others.^[29][30][31] Some Christians historically abstained from meat on All Hallows’ Eve, a tradition reflected in the eating of certain vegetarian foods on this vigil day, including apples, potato pancakes, and soul cakes.^{[32][33][34][35]}