Halloween is a holiday that has its roots in the ancient Celtic festival of Samhain. The festival marked the transition from the warm, fruitful summer months to the cold and dark winter, a period that was most often associated with death. It was believed that on the night of October 31, the boundary between the living world and the world of the dead became thin, and ghosts could return to walk the earth. People dressed in costumes and lit bonfires to ward off spirits. Over time, the holiday evolved and became increasingly secular, with its religious trappings all but disappearing. Today, Halloween is considered a holiday for dress-up and fun, especially for children.

Here are some of the classic Halloween traditions and their origins:

• Carving Jack-o’-Lanterns: This tradition comes from the Irish legend of Stingy Jack, who tricked the devil and was doomed to wander the earth with only a carved-out turnip to light his way.

• Trick-or-Treating: There are several theories about the origins of this tradition. One theory suggests that during Samhain, Celtic people would leave food out to appease the spirits traveling the Earth at night. Over time, people began to dress as these unearthly beings in exchange for similar offerings of food and drink. Another theory argues that modern American trick-or-treating stems from “belsnickeling,” a German-American Christmas tradition where children would dress in costume and then call on their neighbors to see if the adults could guess the identities of the disguised. In one version of the practice, the children were rewarded with food or other treats if no one could identify them.

• Black Cats: Black cats have long been associated with witches and Halloween. In the Middle Ages, they were believed to be witches familiars, or animal companions. This belief led to the persecution and killing of black cats.

• Playing Pranks: The pre-Halloween tradition known as “Devil’s Night” is credited to a different origin depending on the source. Some say that pranks started as part of May Day celebrations. But Samhain, and eventually All Souls Day, also included good-natured mischief. When Irish and Scottish immigrants came to America, they brought with them the tradition of celebrating Mischief Night as part of Halloween.

In the early 20th century, the custom of trick-or-treating, in which children dress up in costume and solicit treats from neighbors, became popular in the United States as Irish and Scottish communities revived th...