Dressing up in costumes and going "guising" was prevalent in Scotland and Ireland at Halloween by the late 19th century. A Scottish term, the tradition is called "guising" because of the disguises or costumes worn by the children. In Ireland the masks are known as 'false faces'. Costuming became popular for Halloween parties in the US in the early 20th century, as often for adults as for children, and when trick-or-treating was becoming popular in Canada and the US in the 1920s and 1930s.