The Halloween holiday has its roots in the ancient Celtic festival of Samhain (a Gaelic word pronounced “SAH-win”), a pagan religious celebration to welcome the harvest at the end of summer, when people would light bonfires and wear costumes to ward off ghosts.

The wearing of costumes at Halloween may come from the belief that supernatural beings, or the souls of the dead, roamed the earth at this time. The practice may have originated in a Celtic festival, held on 31 October to mark the beginning of winter.

Halloween candy wasn't always popular. It began in the 1920s and 30s, becoming more of a tradition in the 1950s as manufacturers aggressively promoted the sale of candy during a sugar shortage.

In Ireland, people started to carve demonic faces out of turnips to frighten away Jack's (a demonic figure) wandering soul. When Irish immigrants moved to the U.S., they began carving jack-o'-lanterns from pumpkins, as these were native to the region.

The history of trick-or-treating traces back to Scotland and Ireland, where the tradition of guising, going house to house at Halloween and putting on a small performance to be rewarded with food or treats, goes back at least as far as the 16th century, as does the tradition of people wearing costumes at Halloween.