Halloween, or All Hallow's Eve, is celebrated on October 31st, originating from Celtic traditions and brought to the U.S. by Irish and Scottish immigrants in the 19th century. The holiday includes activities like trick-or-treating, pumpkin carving, and wearing costumes, with children collecting candy while dressed in various outfits. Common symbols of Halloween include ghosts, jack-o-lanterns, and various spooky creatures.