Halloween originated from the ancient Celtic festival of Samhain, where people would light bonfires and wear costumes to ward off ghosts. In the 8th century, Pope Gregory III designated November 1 as All Saints Day, incorporating traditions from Samhain. Halloween is now celebrated annually on October 31 through activities like trick-or-treating, carving jack-o-lanterns, wearing costumes, and eating sweets. Americans began the tradition of trick-or-treating by dressing in costumes and going door-to-door asking for food or money.