the narrowing of the body between the ribs and hips
A tailoring term usually describing the line that encircles the narrowest part of the waist, but sometimes describing a line above or below this point that is arbitrarily designated according to the silhouette that is popular at the time
The waistline is the line of demarcation between the upper and lower portions of a garment, which notionally corresponds to the natural waist but may vary with fashion from just below the bust to below the hips. The waistline of a garment is often used to accentuate different features. The waistline is also important as a boundary at which shaping darts (such as those over the bust and in the back) can be ended.