What we call "Halloween" (literally, "Holy Evening"), the ancient Celts called Samhain, or "Summer's End." It was believed that the line between this world and the next was thinnest on this night, and that spirits, both good and bad, could cross over. The custom of dressing in disguises was meant to protect against the evil spirits.
Samhain was also considered the Celtic New Year, as it began a new cycle. The other major holiday was Beltaine in the spring. In modern times, we call it May Day. But Samhain, on November Eve, marked the principal calendar feast of the Celtic year. The Druids would light bonfires to usher in the light of a new year.
In modern-day American, Halloween marks the official start of the holiday season, which extends for the next two months and concludes, appropriately enough, on New Year's Day.
Another year gone by. Boo!