Halloween is a contraction of All Hallows Eve. In the 5th Century B.C., in Celtic Ireland, summer officially ended on that day. The holiday was called Samhain (sow-en) meaning “end of summer.”
The custom of Halloween was brought to America in the 1840’s by Irish immigrants fleeing The Great Hunger. At that time the favorite tricks or pranks included tipping over outhouses and unhinging fence gates.
Legend has it that the Jack-o-lantern custom comes from Irish folklore. The tale goes, a man named Jack who was notorious as a trickster tricked Satan into climbing a tree. Jack then carved an image of a cross in the tree’s trunk, trapping the devil up the tree. Jack made a deal with the devil that if he would never tempt him again he would promise to let him down the tree.
According to the folk tale, after Jack died he was denied entrance into heaven because of his evil ways, but he was also denied access to hell because he had tricked the devil. Instead the devil gave him a single ember to light his way through the frigid darkness. The ember was placed inside a hollowed-out turnip to keep it glowing longer.
The Irish used turnips as their “Jack’s lanterns” originally. But when the immigrants came to America, they found that pumpkins were far more plentiful than turnips. So, the Jack-o-lantern in America was a hollowed-out pumpkin, lit with an ember. Source: Anon