Halloween, or Hallowe'en (/?hæl??wi?n, -o??i?n, ?h??l-/: a contraction of All Hallows' Evening), also known as Allhalloween, All Hallows' Eve, or All Saints' Eve, is a celebration observed in a number of countries on 31 October, the eve of the Western Christian feast of All Hallows' Day. See wikipedia for more details.