Halloween is a celebration observed in many countries on 31 October, the eve of the Western Christian feast of All Hallows’ Day. It is at the beginning of the observance of Allhallowtide, the time in the Christian liturgical year dedicated to remembering the dead, including saints (hallows), martyrs, and all the faithful departed. In popular culture, Halloween has become a celebration of horror and is associated with the macabre and the supernatural.

from Wikipedia: Halloween – Wikipedia