This is an excessive forward curvature of the spine in older people, often older women. It’s caused by a combination of genetics, aging, and behavioral factors, such as chronic poor posture.
A “dowager” is a widow who holds property from a deceased husband (a dowry). It’s sometimes used to refer to older women in general, especially those with wealth or aristocratic title.
The connection to the medical condition is that a Dowager’s Hump often manifests in older women, due to the effects of osteoporosis.
Why I Looked It Up
I can’t remember the book, but a character was described as having a “widower’s hump” (the character was male – if she was female, would it have been “widow’s hump”?) Searching that led me to Dowager’s Hump.