This cross quarter day marks the midpoint between the fall equinox and the winter solstice in December. It is traditionally observed on October 31st, a week before the astronomical cross-quarter, and heralds the darker part of the year.

Across Western Christianity, this transition into darkness inspires remembrance of, or communion with, the dead. Eastern Orthodox and Coptic Catholics follow other calculations for their equivalent solemnities, suggesting regional folk practices (including those of the Slavs and Celts) influenced Roman Catholicism as it progressed northward from Rome.