Halloween, celebrated each year on October 31, is a mix of ancient Celtic practices, Catholic and Roman religious rituals and European folk traditions that blended together over time to create the holiday we know today. Straddling the line between fall and winter, plenty and paucity and life and death, Halloween is a time of celebration and superstition. Halloween has long been thought of as a day when the dead can return to the earth, and ancient Celts would light bonfires and wear costumes to ward off these roaming ghosts. The Celtic holiday of Samhain, the Catholic Hallowmas period of All Saints' Day and All Souls' Day and the Roman festival of Feralia all influenced the modern holiday of Halloween.
In the 19th century, Halloween began to lose its religious connotation, becoming a more secular community-based children's holiday. Although the superstitions and beliefs surrounding Halloween may have evolved over the years, as the days grow shorter and the nights get colder, people can still look forward to parades, costumes and sweet treats to usher in the winter season.
Reference: http://www.history.com/topics/halloween
