The Origins of Halloween (Source: Wikipedia)

Halloween is a holiday that is celebrated on the night of October the 31st. Halloween activities include:
Trick-or-treating
“Trick-or-treating” is an activity for children in which they proceed from house to house in costumes, asking for treats such as sweets with the question, "Trick or treat?". The "trick" part of "trick or treat" is a threat to play a trick on the homeowner or his property if no treat is given. It has become socially expected that if one lives in a neighborhood with children one should purchase treats in preparation for trick-or-treaters.
Ghost tours
The term “ghost tour” refers to a series of visits to places that are said to be haunted by ghosts.
Bonfires
A bonfire is a large controlled outdoor fire. The word is a contraction of “bone fire”. The practice is believed to derive from the Celtic festival Samhain (=Halloween), when animal bones were burnt to ward off evil spirits.
Costume parties = fancy dress parties
Costume parties are types of parties where guests dress up in a costume.
Visiting “haunted houses”
A house in which supernatural phenomena occur such as the visits of ghosts or malevolent entities.
Reading scary stories
Carving Jack-o'-lanterns or Jack o' lantern
Throughout Ireland and Britain, there is a long tradition of carving lanterns from vegetables, particularly the turnip and the pumpkin. But not until 1837 does jack-o'-lantern appear as a term for a carved vegetable lantern. And the carved lantern does not become associated specifically with Halloween until 1866 in North America:
The term jack-o'-lantern originally meant a night watchman, or a man with a lantern.

The Irish Legend of Jack O'Lantern:
And there is also an old Irish folk tale that tells of Jack, a lazy yet shrewd farmer who uses a cross to trap the Devil:
One story says that Jack tricked the Devil into climbing an apple tree, and once he was up there Jack quickly placed crosses around the trunk or carved a cross into the bark, so that the Devil couldn't get down.
Another myth says that Jack put a key in the Devil's pocket while he was suspended upside-down.
Another version of the myth says that Jack was getting chased by some villagers from who he had stolen, when he met the Devil, who claimed it was time for him to die. However, the thief stalled his death by tempting the devil with a chance to bedevil the church-going villagers chasing him. Jack told the Devil to turn into a coin with which he would pay for the stolen goods (the Devil could take on any shape he wanted). Later, when the coin/Devil disappeared, the Christian villagers would fight over who had stolen it. The Devil agreed to his plan. He turned himself into a silver coin and jumped into Jack's wallet, only to find himself next to a cross Jack had also picked up in the village. Jack closed the wallet tight, and the cross stripped the Devil of his powers. And so he was trapped. In both myths, Jack only lets the Devil go when he agrees never to take his soul. After a while the thief died, as all living things do. Of course, his life had been too sinful for Jack to go to heaven. However, the Devil had promised not to take his soul, and so he was barred from hell as well. Jack now had nowhere to go. He asked how he would see where to go, as he had no light, and the Devil mockingly tossed him an ember that would never burn out from the flames of hell. Jack carved out one of his turnips (which was his favourite food), put the ember inside it, and began endlessly wandering the Earth for a resting place. He became known as “Jack of the Lantern”, or Jack-o'-Lantern.
There are variations on the legend: Some versions include a “wise and good man”, or even God helping Jack to prevail over the Devil. There are different versions of Jack's bargain with the Devil. Some variations say the deal was only temporary but the Devil, embarrassed and vengeful, refuses Jack's entry to hell after Jack dies. Jack is considered a greedy man and is not allowed into either heaven or hell, without any mention of the Devil. And in some variations it is God himself who gives Jack the turnip.

Irish immigrants carried versions of the tradition to North America in the nineteenth century.

Other western countries embraced the holiday in the late twentieth century.

Today, Halloween is celebrated in several countries of the Western world, most commonly in Ireland (where it originated), the United States, Canada, Puerto Rico, the United Kingdom, New Zealand, and occasionally in parts of Australia.

Halloween has its origins in the ancient Celtic festival known as Samhain. The festival of Samhain is a celebration of the end of the harvest season in Gaelic culture, and is sometimes regarded as the “Celtic New Year”. Traditionally, the festival was a time used by the ancient pagans to take stock of supplies and slaughter livestock for winter stores. The ancient Gaels believed that on October 31st, now known as Halloween, the boundary between the alive and the deceased dissolved, and the dead became dangerous for the living by causing problems such as sickness or damaged crops. The festivals would frequently involve bonfires (bone fires), where the bones of slaughtered livestock were thrown. Costumes and masks were also worn at the festivals in an attempt to mimic the evil spirits or placate them.
The term Halloween is shortened from All-hallow-evening, as it is the eve of “All Hallows'Day”, also known as “All Saints'Day”. It was a day of religious festivities in various northern European Pagan traditions, until Popes Gregory III and Gregory IV moved the old Christian feast of All Saint's Day from May 13 to November the first. Although All Saints' Day is now considered to occur one day after Halloween, the two holidays were, at that time, celebrated in accordance to one another.

Halloween did not become a holiday in the United States until the 19th century, where lingering Puritan tradition restricted the observance of many holidays. The transatlantic migration of nearly two million Irish following the Irish Potato Famine (1845-1849) finally brought the holiday to the United States. Scottish emigration, primarily to Canada before 1870 and to the United States thereafter, brought the Scottish version of the holiday to each country. And The commercialization of Halloween in the United States did not start until the Xxth century.