Halloween as we know it today, is a derivation of “All Hallows’ Evening” or All Saints’ Eve. This is a yearly celebration observed in a number of countries on 31 October, the eve of the Western Christian feast of All Hallows’ Day.
It initiates the three days of Allhallowtide, the time in the liturgical year dedicated to remembering the dead, including saints (hallows), martyrs, and all the faithful departed believers.
Within Allhallowtide, the traditional focus of All Hallows’ Eve revolves around the theme of using humour and ridicule to confront the power of death. Typical festive Halloween activities include trick-or-treating (or the related “guising”), attending costume parties, decorating, carving pumpkins into jack-o’-lanterns, lighting bonfires, apple bobbing, visiting haunted house attractions, playing pranks, telling scary stories, and watching horror films (source: http://en.wikipedia.org/wiki/Halloween).
Happy trick or treating!