The circumference measurement taken around the fullest part of the buttocks and hips, typically located 7 to 9 inches below the natural waistline. In pattern drafting, it serves as a critical horizontal anchor for shaping skirts, trousers, and dresses. Getting the hipline right ensures the garment hangs cleanly without riding up or pulling.
Heard on the job
The skirt is pulling across the front because there isn't enough ease at the hipline.