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.