What accessory is used to hold up stockings or socks?

A garter is an article of clothing comprising a narrow band of fabric fastened about the leg to keep up stockings. In the eighteenth to twentieth centuries, they were tied just below the knee, where the leg is most slender, to keep the stocking from slipping. The advent of elastic has made them less necessary from this functional standpoint, although they are still often worn for fashion. Garters have been widely worn by men and women, depending on fashion trends.

Source: Wikipedia