Halloween is a holiday in many English speaking countries that is celebrated on the night of October 31st. Children wear costumes and they go to  homes saying “Trick or treat!” to ask for candy, sweets in the United Kingdom, or lollies in Australia. This practice originally involved a threat. In this case the threat could be explained as: “Give me a treat or I will play a trick on you”. Children today usually do not play tricks if they do not get treats. However, some children still get up to mischief (pranks or things to make fun of people; like putting toilet paper in trees; writing on windows with soap or throwing eggs at peoples’ houses). People sometimes dress up as ghosts, witches, goblins and other scary things for Halloween.

To be more specific:

Halloween or Hallowe’en ( a contraction of “All Hallows‘ Evening“),also known as All Hallows’ Eve, is a yearly celebration observed in a number of countries on October 31, the eve of the Western Christian feast of All Hallows (or All Saints) and the day initiating the triduum of Hallowmas, the time in the liturgical year dedicated to remembering the dead, including saints (hallows), martyrs, and all the faithful departed believers.