Women traditionally wear girdles to improve the appearance of their figure. Wikipedia explains that girdles took the place of corsets as the common garment used to support the torso and give the appearance of a slimmer waist. However, after the 1960s, girdles became less popular and were generally replaced with other supportive under garments, such as pantyhose.
During the modern decades when girdles were widely used, between the 1920s and 1960s according to Wikipedia, the figure of a slim-waisted woman was regarded as representing modesty and respectability. Today, many women still opt for undergarments that enhance body shape, popularly referred to as shapewear.
However, girdles or shapewear merely use pressure to give the appearance of a flat torso. Mayo Clinic explains that this effect is only temporary, as these garments do not actually strengthen the muscles or trim the fat underneath. Exercising and dieting are necessary for women who want their abdomen to be trim and flat even without wearing a girdle. To achieve this, women should engage in fat-burning aerobic activity and also attempt exercising the core muscles with crunches. Healthy changes in diet can also help naturally improve the appearance of a woman's figure, especially around the abdomen.