Umbilical hernia is a type of abdominal wall defect that occurs when part of the intestine or other tissue protrudes through an opening near the navel. It is most common in infants and young children, but it can also occur in adults. Symptoms include a bulge near the navel, pain or discomfort when coughing or straining, and nausea. Treatment usually involves surgery to repair the hernia and prevent further complications.