(AKA All Hallows' Eve)
The “Hallows” part of the name means “Saints.” The origin of the holiday is a commemoration of the end of summer and the beginning of the darker half of the year.
Ancient Celts believed that the wall between life and afterlife became thin at this time, and so spirits both good and evil could cross over to the normal world. The idea of wearing costumes and masks is to ward off the harmful spirits, and people also carved faces into hollowed-out turnips, which were lit from inside with candles and placed in windows—again to keep harmful spirits away. (A turnip jack-o-langtern is pictured here, below right.) Bonfires were often used during the festivities.
As is always the case, the holiday changed and evolved. In North America, pumpkins were easier to find than were turnips—and pumpkins are of course much larger and easier to carve as well!
Trick or treating started with the custom of poor people going from door to door, getting gifts of food, on November 1. Although some of these ritual “begging” customs date all the back to the middle ages, American children in costumes going from shop to shop or door to door only started in the early 1900s.
Many of the symbols of Halloween come from the Day-of-the-Dead (All Saints' Day) imagery of skeletons. Others come from popular monster lore such as Frankenstein and Dracula, and of course many decorations and themes are related to harvest time (scarecrows, apple bobbing, pumpkins).
Modern Halloween practices in the U.S. often include “haunted” attractions such as haunted houses, theme parks remade into scary mazes, corn mazes and hayrides, and more. In some cases high levels of special effects are used, and scaring people has become big business. Where I live, in Southern California, people have SO many choices, including the famous Knott's Scary Farm, but also Halloween Horror Nights at Universal Studios, Fright Fest at Six Flags Magic Mountain, Shipwreck at the Queen Mary, Castle Dark (at Riverside's Castle Park), Fearplex Haunt (at Pomona's Fairplex)—and many, many more. (Hmmm...I like the names Coffin Creek and the Scream Zone—haven't heard of those ones before...)
The Spread of Halloween
This holiday started with ancient Celtic peoples in the British Isles, and is still celebrated by many in England, Scotland, and Ireland, but it boomed in a big way in the United States and Canada, while the Day of the Dead blossomed in Mexico. Nowadays much of the North American celebrations seems to be spreading to other parts of the world, including South America, Europe, Australia, and Japan.
Probably much of the spread of Halloween is because of depictions in Hollywood movies and on television. Nowadays Halloween as a celebration for children is becoming quite popular.