The abdominal wall is a sheet of tough muscle and tendon that runs between your ribs and your groin. It acts like a natural corset holding all the abdominal organs in place. There are natural weaknesses in the abdominal wall, eg where the blood vessels and nerves pass through. Sometimes, this weakness opens up so whatever is on the inside(usually part of the gut) pushes through. This causes a bulge or swelling called a hernia.