腰线 (yāo xiàn) literally combines 腰 (yāo), meaning 'waist', and 线 (xiàn), meaning 'line'. It refers to the natural horizontal contour of the body at the narrowest part of the torso — the waistline — or, in clothing design, the stitched or decorative horizontal line on a garment that corresponds to or emphasizes that anatomical point. Unlike abstract measurements, 腰线 conveys a visual and functional boundary: it’s where belts sit, where skirts flare, or where jackets end.

This term appears frequently in fashion descriptions, fitness discussions, and medical or ergonomic contexts (e.g., posture analysis). It is neutral in register and used in both spoken and written Chinese. While it can refer to the body’s physical waistline, it is more commonly used when discussing garment fit, tailoring, or body proportion — for example, saying a dress ‘has a high waistline’ (高腰线) implies the seam sits above the natural waist for a flattering silhouette.