Samhain is a Gaelic festival marking the end of the harvest season and the beginning of winter, traditionally celebrated from October 31 to November 1. It is believed to be a time when the boundary between the living and the dead is blurred, allowing spirits to roam the earth. The festival has roots in ancient Celtic traditions and has influenced modern celebrations of Halloween. Samhain involves various customs, including bonfires, feasting, and honoring ancestors.