All Hallows' Eve, short for All Hallows' Evening, is a less common name for the holiday of Halloween. It takes place each year on Oct. 31.
Originally a Christian celebration, All Hallows' Eve began in the late 18th century. The holiday takes place the day before All Saints' Day and two days before All Souls' Day. These three days make up Allhallowtide, a time which focuses on remembering the dead and honoring saints. Some historians believe that the holiday was heavily influenced by Celtic pagan traditions. Modern celebrations often involve activities such as trick-or-treating and wearing costumes, which have distant roots in Medieval traditions.