Protrusion of any organ or tissue from its normal cavity. The term usually refers to an abdominal hernia, which may be a congenital disorder or acquired after birth. Tissue may protrude through the abdominal muscle at the groin (inguinal), upper thigh (femoral), or navel (umbilical); its circulation can become cut off, leading to inflammation, infection, and gangrene. If the tissue cannot be pushed back into place and kept there by a truss, surgery may be necessary. Other common hernias are hiatal hernia (protrusion of part or all of the stomach above the diaphragm) and herniated disk (protrusion of tissue from a disk in the vertebral column through its outer layer).