Hallowe'en, also known as All Hallow's Eve or Halloween, is a holiday celebrated on 31 October.
Hallowe'en is a date for great celebrations at Hogwarts School of Witchcraft and Wizardry. Entertainment is provided by ghosts and a feast is held in the Great Hall on this day.
In 1992, a group of ghosts held a Deathday Party in celebration of the 500th deathday of Sir Nicholas de Mimsy-Porpington. The party was attended by Harry Potter, Ron Weasley and Hermione Granger.
Harry Potter's parents were murdered by Lord Voldemort on Hallowe'en. Voldemort then attempted the same curse on Harry, only for it to rebound and reduce him to a spectral state.