Halloween wasn’t always Halloween. It was first called Samhain. Samhain, a Celtic festival still celebrated by pagans, means “summer’s end.” Samhain celebrates the end of what is considered the “lighter half” of the year (spring and summer) and the beginning of the “darker half” of the year (fall and winter).
What about the actual word “Halloween?” Halloween is a variant of All Hallows Evening, which, on Oct. 31, is the day before All Hallows Day on Nov. 1. This was shortened to All Hallows Even, and then the “v” was dropped to All Hallows E’en. It’s not a big jump to see how that got to Halloween.