Hernia: A general term referring to a protrusion of a tissue through the wall of the cavity in which it is normally contained.
More specifically, a hernia often refers to an opening or weakness in the muscular structure of the wall of the abdomen. This defect causes a bulging of the abdominal wall. This bulging is usually more noticeable when the abdominal muscles are tightened, thereby increasing the pressure in the abdomen. Examples of activities that can worsen a hernia are lifting, coughing, or even straining to have a bowel movement. Imagine a barrel with a hole in its side and a balloon that is blown up inside the barrel. Part of the inflated balloon would bulge out through the hole. The balloon going through the hole is like the tissues of the abdomen bulging through a hernia.
Symptoms of a hernia include pain or discomfort and a localized swelling somewhere on the surface of the abdomen or in the groin area.
Serious complications from a hernia result from the trapping of tissues in the hernia -- a process called incarceration. Trapped tissues may have their blood supply cut off, leading to damage or death of the tissue.
The treatment of incarceration requires immediate surgery.
For a full article on this subject, see Hernia.