Halloween or Halowe’en comes from All Hallows Eve – The night before All Hallows Day (All Saints Day) which was the Christanisation of Samhain an ancient Celtic festival of celebration, feasting and connecting with ancestors at harvest time. Celebrated on October 31st, the half way point between the Autumn Equinox and Winter Solstice. Ancient Celtic tradition marked this as a time when the barriers between the spiritual and physical worlds came down which marked it as a time for Fairies (Shee/Sidhe) and other malevolent beings. From here we get many of the pagan practices that continue to today. Irish and Scottish migrants took their traditions with them to America and America, well Americanised it.
Links to past Jack O’ Lanterns 2017 here https://www.tonyoneill.org/2017/10/25/traditional-jack-o-lantern-2017/ and 2016 here http://www.tonyoneill.org/2016/10/27/irish-jack-o-lantern/