Halloween is a holiday celebrated on the night of October 31, from sunset to sunrise. On this day, people dress up in costumes and go from door to door asking for candy while saying "trick-or-treat!" The word "hallowe'en" comes from All Hallows' Eve, meaning the evening before All Saints' Day. In the United States and Canada, children usually go trick-or-treating on Halloween.
The origins of Halloween are probably Celtic in origin but it's unclear what old Celtic tradition may have been displaced.