In general terms, we can say that a hernia occurs when the layers that make up the abdominal wall weaken. In other words, the fabric of muscle and other tissues which protect the gut, develops a defect, or weakness. Through that defect the peritoneum (PER-IT-TA-NEE-UM) - and perhaps other organs - push their way outward, forming a lump which can be felt - and sometimes seen - protruding from the abdomen.