Halloween or Hallowe’en (less commonly known as Allhalloween,^[5] All Hallows’ Eve,^[6] or All Saints’ Eve)^[7] is a celebration observed in many countries on 31 October, the eve of the Western Christian feast of All Saints’ Day. It begins the observance of Allhallowtide,^[8] the time in the liturgical year dedicated to remembering the dead, including saints (hallows), martyrs, and all the faithful departed.^{[9][10][11][12]}

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.^{[13][14][15][16]} Some go further and suggest that Samhain may have been Christianized as All Hallow’s Day, along with its eve, by the early Church.^[17] Other academics believe Halloween began solely as a Christian holiday, being the vigil of All Hallow’s Day.^{[18][19][20][21]} Celebrated in Ireland and Scotland for centuries, Irish and Scottish immigrants took many Halloween customs to North America in the 19th century,^[22][23] and then through American influence Halloween had spread to other countries by the late 20th and early 21st century.^[24][25]

Popular Halloween activities include trick-or-treating (or the related guising and souling), attending Halloween costume parties, carving pumpkins or turnips 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.^[26] Some people practice the Christian religious observances of All Hallows’ Eve, including attending church services and lighting candles on the graves of the dead,^[27][28][29] although it is a secular celebration for others.^[30][31][32] 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.^{[33][34][35][36]}