Costume parties where people dress up in a variety of fancy dress outfits are now most commonly held during Halloween celebrated on the 31st October. The name comes from the feast of All Hallows or All Saints Day celebrated on the 1st November in honor of all the saints. The Halloween festival is actually a celebration of the end of the harvest in Gaelic culture and spread to America with the Irish immigrants and became part of popular culture.
Halloween traditions include 'trick or treating', making bonfires, visiting haunted houses and of course dressing up in fancy dress costumes and attending costume parties. Halloween fancy dress themes usually involve dressing up in a scary fancy dress costume like traditional ghost costumes and witch costumes. More modern alternatives like the scary movie ghost costumes, Dracula and other vampire costumes, Darth Vader Costumes, Skeleton Costumes and other scary film characters like The Addams family and Leatherface, the star of The Texas Chainsaw Massacre are becoming increasingly popular.
Taken from http://antiquedress.blogspot.com/