More than a thousand years ago the Christian church named November 1 All Saints Day (also called All Hallows.) This was a special holy day to honour the saints and other people who died for their religion. The night before All Hallows was called Hallows Eve. Later the name was changed to Halloween.
Like the Celts, the Europeans of that time also believed that the spirits of the dead would visit the earth on Halloween. They worried that evil spirits would cause problems or hurt them. So on that night people wore costumes that looked like ghosts or other evil creatures. They thought if they dressed like that, the spirits would think they were also dead and not harm them.
So - we are gonna have a massive Hallowe'en Ball - Full Fancy Dress & DJ's