Halloween, one of the oldest and most popular holidays, is an annual celebration on October 31. Dating back 2,000 years, it has roots in the Celtic pagan festival Samhain and the Christian All Saints Day, though it is largely a secular celebration today. Around the time of the Great Famine, Irish immigrants brought varieties of many Halloween traditions to North America.
The name is derived from All Hallows' Even. Even is derived from evening, which can be further shortened to e'en. Hence, the holiday's original name of Hallowe'en.
The feast of Samhain, honoring the dead, was held every October 31, the end of the Celtic calendar. A harvest festival, Samhain signified the end of summer with huge bonfires. Believing that souls of the dead roamed the streets and villages, and that not all were friendly, Celts set out gifts or treats to pacify them. This is where our tradition of trick-or-treating comes from.