细腰 (xì yāo) literally means 'thin waist' or 'slim waist' — 细 (xì) means 'fine', 'slender', or 'narrow', and 腰 (yāo) means 'waist'. Together, they form a compound noun describing a noticeably narrow or gracefully slender waistline. Though occasionally used in human fashion or body description, this term is most commonly found in zoology and classical Chinese literature to describe the physical anatomy of certain animals — especially insects like wasps and dragonflies, whose bodies feature a distinctly constricted segment between thorax and abdomen.

In modern usage, 细腰 retains its descriptive precision but carries subtle aesthetic or poetic connotations, often implying elegance, fragility, or natural grace. It rarely appears in casual speech about people today; instead, terms like 小蛮腰 (xiǎo mán yāo) or 纤腰 (xiān yāo) are more common in literary or complimentary contexts. The phrase is neutral in register but leans formal or technical when applied to animals.