Halloween 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 triduum of Hallowmas, the time in the liturgical year dedicated to remembering the dead, including saints (hallows), martyrs, and all the faithful departed believers. Halloween costumes are traditionally modeled after supernatural figures such as vampires, monsters, ghosts, skeletons, witches, and devils. Over time, in the United States the costume selection extended to include popular characters from fiction, celebrities, and generic archetypes such as ninjas and princesses.