The waistline is the part of a piece of clothing that sits on the wearer's waist. The actual position of the waitline can be different depending on the fashion or how the person chooses to wear the garment, but it is normally just above the hips.
Images for kids
Joséphine de Beauharnais wearing a dress with an empire waist.
Waistline (clothing) Facts for Kids. Kiddle Encyclopedia.