Halloween is one of the most popular holidays in the United States. It is celebrated for a number of days before Halloween and continues on until the night of Halloween itself. The word "Halloween" in addition to its related Greek terms "othei," means "truce." Halloween had its origin in the Pagan festival of Samhain amongst the Celts of ancient Britain and Ireland. On that day, which corresponds to October 31 on modern calendars, the old year was thought to be over.