Samhain was originally a Fall harvest festival that traditionally occurred after the first frost killed the grass and excess cattle were slaughtered because it was cool enough for the meat to keep. The bones of the cattle were thrown into the bonefire, the term from which we take the modern term, bonfire. The bonefire was also a time of remembering the dead, community bonding, ritual purification, and divination. As was its practice, when the Roman Catholic Church encountered Celtic polytheism it Christianized these pagan observances, creating All Saint's Eve and All Saint's Day which are still observed as Halloween.
If you plan to consume ethanol at this year's festivities, please designate a driver. Do not drink and drive. Have a plan, stay alive.