A hernia is defined as the protrusion of an organ or tissue through a defect or weakness in its containing wall, most commonly in the abdominal wall. This defect allows intra-abdominal contents, such as intestines or fat, to bulge outward, which can lead to complications like incarceration or strangulation. Surgical repair focuses on closing the defect and reinforcing the wall to prevent recurrence. Understanding this fundamental definition is crucial in differentiating hernias from tumors, infections, or vascular issues, which have distinct pathophysiologies and treatments.

Reference: Sabiston Textbook of Surgery, Townsend CM, 21st Edition.