This is the third and last pagan harvest festival. The moon is waning, two days short of new. Not what one normally thinks of when "harvest festival" comes around. The "Harvest Moon" actually comes in September, this year September 17th. The full moon in October is called the "Blood Moon" or "Hunter's Moon".
Halloween as practiced in the United States is an amalgam of practices. The name, Halloween, is derived from Hallow's eve, or the day before All Hallows Day, the day Roman Catholics, and later, other Christian groups, celebrate all saints, specified and unspecified. The Irish brought their Celtic-derived observance of seasonal change and festival of the dead. Pagans celebrate "samhain," and in true Celtic fashion, it has a pronunciation totally at odds with its current spelling: "sow-in," rhymes with "cow-in." It comes from the Gaelic "sam," which means summer; "fuin" means "end." So, "Samhain" means "end of the warm season." Contrary to many web sites, there is and has never been a god of death or a sun god with that name.
Many believe the door between this world and the next is thinner at this time. This has resulted in beliefs ranging from evil spirits roaming the earth in search of bodies to take or souls to steal. Others believe this is the time to contact those who have gone before, looking for guidance or just to pay their respects.