Originally, masks were part of the traditions of Samhain, the Celtic harvest festival that has evolved into Halloween. During Samhain, masks were created and worn by the living as a form of protection, and camoflage, amongst the ghosts and ghouls. Today, they are worn as part of a costume, at parties or while trick-or-treating. They may also be placed on walls as decorations.
A mask can be as simple as two eyeholes in a decorated paper plate, a store-bought ghoul mask, or as complex as the impressive latex creations of movie monsters.