When the breast bone is caved in.
depression of the breastbone (sternum) and rib cartilages
Concave chest (caved in) opposite of pectus carinatum.
A defect of the sternum that's present at birth.
Pectus excavatum is a congenital deformity (often present at birth) of the sternum, which is depressed into the chest, resulting in a "caved-in" or sunken appearance.