Halloween is a celebration observed on October 31, the eve of the Western Christian feast of All Hallows' Day, also known as All Saints' Day. It marks the beginning of Allhallowtide, a Christian time dedicated to remembering the dead, including saints and martyrs. Historically, Halloween has roots in the ancient Celtic festival called Samhain, celebrated around November 1, which signified the end of the harvest and the start of winter. The Celts believed that on this night the veil between the living and the dead was thinnest, allowing spirits to return to the earth. To ward off these spirits, people would light bonfires and wear costumes. Later, Christian leaders established All Saints Day on November 1 to replace or coincide with these pagan traditions, and the evening before became known as All Hallows' Eve, eventually shortened to Halloween. Today, Halloween is largely secular and celebrated with activities like trick-or-treating, costume parties, carving pumpkins into jack-o'-lanterns, telling scary stories, and attending haunted attractions. Children commonly dress in costumes and go door-to-door asking for candy. While some Christians still observe the religious aspects by attending church or lighting candles for the dead, for many it is a day focused on fun, fright, and community festivities. Halloween traditions spread widely across the U.S., Canada, and other countries largely due to Irish and Scottish immigrants in the 19th century, with the holiday evolving into the playful celebration known today.