bad back; spineless person
Used both literally for a weak or painful lower back and figuratively for a person who lacks resolve or easily gives in. The figurative use is colloquial and somewhat derogatory.
最近、腰弱で長時間座っていられない。
Lately, my bad back makes it hard to sit for long periods.
彼
He's spineless, so he gives in quickly during negotiations.
Compound of 腰 (lower back) and 弱 (weak). The figurative sense likely derives from the idea that a weak back cannot support a firm stance, metaphorically extending to a lack of resolve.