Protrusion of the viscera through the peritoneum or mesentery and into a compartment in the abdominal cavity.  
Most common presentation is an acute  intestinal obstruction of small bowel loops that develops through normal or abnormal apertures.
Responsible hernial orifices are usually preexisting anatomic structures, such as foramina, recesses, and fossae.
Pathologic defects of the mesentery and visceral peritoneum, which are caused by congenital mechanisms, surgery, trauma, inflammation, and circulation, are also potential herniation orifices.
Internal hernia
Incisional hernia
Inguinal hernia
Indirect inguinal hernia
Direct inguinal hernia
Varicoscele
Spigelian hernia
Enterocele