Your waistline is the narrowest part of your body between your ribs and hips, where your torso naturally curves inward. If you wrap a measuring tape around your middle at belly button level, you're measuring your waistline. This is also where you typically wear the waistband of your pants or skirt.

Tailors and clothing designers care about the waistline because it helps them create clothes that fit well. When you shop for pants, the size often refers to the waist measurement. A pair of jeans might have a 24-inch waistline, meaning the waistband measures 24 inches around.

People also use waistline to talk about body size in general. Someone might say they're “watching their waistline” when they're trying to stay healthy and fit. Doctors sometimes measure waistlines because it can provide information about a person's overall health, just like measuring height or checking heart rate.