腰 covers both the waist and lower back in Chinese — there's no separate everyday word for 'lower back.' 腰疼 can mean either waist pain or lower back pain.
culture
弯腰 (wān yāo, bend at the waist) and 直腰 (zhí yāo, straighten up) are common in Chinese idioms. 腰包 (yāobāo) literally means 'waist bag' — a fanny pack.
