Samhain
The Celts
The ancient Celts divided their year according to astronomical cycles. They recognized, (we think): The Winter Solstice, Spring Equinox, Summer Solstice, and Autumn Equinox as the 4 quarters of the year, and the dates halfway in between each of those dates as the “Cross-Quarters.” The Cross-Quarters, (Imbolc, around February 2, Beltane around May 1, Lughnasadh around August 2, and Samhain, around November 7) were and are the major turning points of the year, and the Quarters are more minor holidays.
The exact halfway point between the Autumn Equinox and the Winter Solstice is Samhain and it falls on November 7th this year, a full week after the non-religious holiday of Halloween.