Halloween, or All Hallows' Eve, comes from the ancient Celtic festival called Samhain and was invented because the Pagans felt that October 31 was the one day out of the year that the boundary between the living and the dead overlapped. They believed the dead would come back to earth and cause illness or damaged crops. At that time, people participating in the Samhain festival would wear costumes and masks in an attempt to mimic evil spirits.
Trick-or-treating is a custom originating in the Middle Ages and one that millions of children still participate in today. The word "trick" was meant as a threat to homeowners that announced the intention of doing damage to property if no treat was given. In some states such as Iowa, Ohio and Massachusetts, trick-or-treating is sometimes called Beggars' Night. Trick-or-treating didn't make it to the United States until 1911.
The Jack-o'-lantern is also common throughout the world although the term for a carved pumpkin varies worldwide. There are several variations as to how this tradition started, but a popular legend involves a lazy farmer who traps the devil in an apple tree. The Jack-o'-lantern first appeared in the mid-17th century and is still a popular Halloween decoration today.