In ancient Ireland, the year was divided by the Celtic calendar into two parts: the dark, and the light. The festival of Samhain took place at the end of the harvest, right at the beginning of winter, when the dark came. It was marked by a three-day festival in which people would celebrate the end of the harvest and prepare for the winter by making sure they had enough food put away. A bonfire was lit in the community, everyone extinguished their home fires, and during the festival all members of the community would bring a torch and get a "new" fire to bring to their homes for the winter. This was said to bind the members of the community together.
Samhain is also related to the ancient festival of the dead. Monday, November 1, is the day of the dead this year.
(The five-point star around the cat's neck, the Pentagram, was considered a connection to God, a symbol of protection)
The Irish believed that during Samhain, the barrier between this world (of the living) and the other world (of the dead) became thin and penetrable, and the dead could return to the living world during that holiday. People would set places at the table for their dead relatives to join them for a meal. It is believed that the habit of creating scary masks and costumes originated because it was supposed to fool any evil spirits who might come from the dead world into the living, and make them think that people were themselves evil spirits and should not be touched.
In modern America, the end of the harvest time is celebrated in most communities by Halloween when children dress up as monsters and ghosts, and go door to door asking for candy. "Trick or treat" is what the children say to the homeowners when they open their front door. The question is this: would you rather that we children play some "trick" on you? Or would you rather give us a "treat," usually candy. In Ireland, the children during this holiday sometimes went door to door performing songs and dances for their neighbors.
The term "Halloween" is derived from an old English term which meant "eve of" All Saints Day. All Saints Day is a Christian Holiday which used to be celebrated in the spring. In around 700-800 A.D., the Catholic Church wanted to eliminate the "Pagan" holidays and rituals of the Irish, and moved All Saints Day from the spring to November 1 in the hopes of substituting it for the Irish festival of Samhain. It didn't work, and eventually Samhain, the modern Halloween (or "eve of All Saints Day), and All Saints Day (sometimes called the Day of the Dead) all became merged and occurred around the same time, at the end of October and early November. All Saints Day is November 1.
Among the current symbols of Halloween which come from Ireland are the practice of lighting candles and displaying them in the front of the house (which was done to recognize the people who were departed from this life), and carving lanterns with faces from vegetables (usually turnips). The term "jack-o-lantern" comes from an Irish tale of an old farmer named Jack who fooled the devil by chasing him up a tree, then carving a cross at the base of the tree. The devil cursed Jack and forced him to wander the earth forever with one candle inside a carved turnip.
In the U.S., the Halloween masks and costumes have been heavily influenced by the movie industry, so that modern monsters such as Frankenstein and Dracula replaced the more traditional Irish masks of vague "spirits." How many Michael Jackson "Thriller" costumes will be sold this year?