Halloween has its origins in the ancient Celtic festival known as Samhain (pronounced “sah-win”).
The festival of Samhain is a celebration of the end of the harvest season in Gaelic culture. They believed during this period, the boundaries between the worlds of the living and the dead overlapped and the deceased would come back to life and cause havoc.
Interestingly; Aboriginal, Anglo-Welsh, Chinese, East Europe, Iberian, South Native Americans, Russian, Northern Teutonic, and South Pacific cultures all have a celebration of some kind for Samhain. Read more here