Trick-or-treating is a Halloween custom where children and adults in some countries dress up in costumes and travel from house to house, asking for treats with the phrase "trick or treat". The "treat" is usually candy or sweets, although in some cultures, money is given instead. The "trick" refers to a threat, usually idle, to perform mischief on the resident(s) or their property if no treat is given. Some people signal that they are willing to hand out treats by putting up Halloween decorations outside their doors, while others leave their porch lights on as a universal indicator that they have candy. The interjection "Trick or treat!" seems to have arisen in central Canada before spreading into the northern and western United States in the 1930s and across the rest of the United States through the 1940s and early 1950s. The custom of trick-or-treating started in the western United States and Canada and slowly moved eastward. Trick-or-treating became widespread in the U.S. after the Second World War, when rationing ended and candy was once again readily available. Today, Halloween trick-or-treating is big business, with over 75 percent of U.S. adults giving out candy every year to trick-or-treaters.