Waistline refers to the horizontal line where the waist is narrowest, or to the general appearance of the waist. People who diet are often said to be trying to "improve" their waistline.
Traditionally belts are worn around the waist.
The size of a person’s waist or waist circumference, indicates abdominal obesity. Excess abdominal fat is a risk factor for developing heart disease and other obesity related diseases. The National, Heart, Lung and Blood Institute (NHLBI) classify the risk of obesity related diseases as high if: men have a waist circumference greater than , and women have a waist circumference greater than .
Waist reduction or waist training refers to the act of wearing a corset or other constricting garment to reduce or alter the waistline. The four floating ribs may be permanently compressed or moved by such garments. A girdle may also be used to alter the appearance of the waist and inhibits one's ability to breathe well.
Waist reduction may be used simply to reduce the width of the waist. This change can be permanent or temporary.
Waist training may be used to achieve a certain permanent waist shape, such as a pipe-stem waist.