‘软肋’ literally means 'soft rib'—referring to the tender, unprotected area beneath the ribs in the human or animal body. Figuratively, it describes a critical weakness or vulnerability that can be easily exploited, much like the Greek myth of Achilles’ heel. The character 软 (ruǎn) means 'soft' or 'weak', while 肋 (lèi) means 'rib'; together, they evoke an anatomical soft spot that symbolizes a strategic or personal flaw.

This term is widely used in both formal and informal contexts: in business strategy (e.g., a company’s operational blind spot), interpersonal dynamics (e.g., an emotional sensitivity), or martial arts and military analysis. Though rooted in physical anatomy, 软肋 is almost always metaphorical in modern usage—and rarely refers to actual anatomy. It carries a slightly literary or rhetorical tone, often appearing in news commentary, management discussions, or psychological observations.