All Hallows Eve
Halloween falls on October 31, which in the old Celtic calendar was the last day of the year, its night being the time when all the witches and warlocks were abroad. On the introduction of Christianity it was taken over as the eve (even or e’en) of All Hallows or All Saints.
Brewers Dictionary of Phrase & Fable
Of course, most young people know that the most important part is “trick or treating” – and the treats are the most important part of all!!
Have fun, enjoy, and be safe.