Halloween dates back to ancient Celtic festival of Samhain (pronounced sow-in), celebrated on November 1 as the new year. It marked the end of summer and harvest before the dark, cold winter. Celts believed that on the night of October 31, the boundary between the worlds of the living and the dead became blurred. They wore costumes, built huge bonfires, and left treats on doorsteps for friendly spirits.
Pope Gregory III expanded the Catholic feast of All Martyrs Day to include all saints, observed on November 1.
Eventually All Saints Day was also called All-hallowmas. The night before it began to be called All-hallows Eve; eventually it was renamed "Halloween."
Today in America, Halloween focuses on trick-or-treating for the young. With an estimated $6 billion spend annually, it has become the country's second largest commercial holiday