bent back; stooping back
Describes a back that is bent or stooped, often due to age or poor posture. The term literally means 'double-layered waist', evoking a folded appearance.
My grandmother walks with a stooped back and seems to have a bit of difficulty.
Years of desk work have given me a bent back.
Compound of 二重 (ふたえ, 'double-layered') and 腰 (こし, 'waist/lower back'), describing a back that appears folded or doubled over.