Halloween is a celebration on the night of October 31. It is most practised in the United States and Canada. Children wear costumes and go to people's homes saying "Trick or treat!" to ask for candy (sweets in the UK) and people give it to them. The suggestion is: "Give me a treat or I will play a trick on you." People mainly dress up as ghosts, witches, or other scary things for Halloween.
For Christians it is the eve of All Saints' Day, which begins the three-day observance of Allhallowtide. This covers the three days – October 31 (All-Hallows Eve or Hallowe'en), November 1 (All Saints) and November 2 (All Souls). All Hallows' Eve is a Christianized feast influenced by Celtic harvest festivals, and pagan roots.
The pagan holiday Samhain, which the All Saints holy day replaced, was also known as the Day of the Dead. Many wiccans and modern pagans celebrate the Day of the Dead. This is a happy holiday (even though it celebrates death). It is the day that some believed the souls of dead people come back to Earth.
During Halloween some people wear a costume. People have worn costumes at Halloween for centuries. Wearing a costume may come from Celtic festivals of Samhain and Calan Gaeaf. It could also be from the Christian Allhallowtide.
Early costumes were usually scary. They were often supernatural beings or from folklore. In the 1930s costumes of characters from literature, radio, or movies became popular. Scary costumes are still popular.