All Hallows' Eve is a celebration observed in a number of countries on the eve of the Western Christian feast of All Hallows' Day. Samhain is a Gaelic, Pagan, and Wiccan festival marking the end of the harvest season and a celebration of the dead and ancestors.
Why is it important?
All Hallows' Eve begins the three-day observance of Allhallowtide, the time in the liturgical year dedicated to remembering the dead, including saints (hallows), martyrs, and all the faithful departed.
The day also coincides with Reformation Day, a Protestant Christian religious holiday celebrated alongside All Hallows' Eve (Halloween) during the triduum of Allhallowtide in remembrance of the onset of the Reformation (the split of the Western Church into Protestantism and what is now the Roman Catholic Church).