Acute abdomen
The abrupt (acute) onset of abdominal pain.
A potential medical emergency, an acute abdomen may reflect a major problem with one of the organs in the abdomen such as the appendix (being inflamed = appendicitis), the gallbladder (inflamed = cholecystitis), the intestine (an ulcer that has perforated), the spleen (that has ruptured), etc.
The term 'acute abdomen' is medical shorthand.
It has nonetheless come into common usage in medical parlance