The Simpsons Halloween episodes
Treehouse of Horror, or The Simpsons Halloween Specials, is a seasonal special TV episode that is aired in every season (except the first one) where there are three different Halloween-based stories. Most of the time the episodes are about something really scary, unusual, or science-fictional event happening to the family. Since they have nothing to do with the real episodes, they are considered non-canonical (things that do not really happen).