In this case, the protrusion is simply abdominal lining or fat. (wagwalking.com)
In many people, the abdominal wall weakness that leads to an inguinal hernia occurs at birth when the abdominal lining (peritoneum) doesn't close properly. (mayoclinic.org)
An umbilical hernia is a protrusion (outward bulging) of the abdominal lining, abdominal fat or a portion of abdominal organ (s) through the area around the umbilicus (navel or belly button). (glenerinanimalhospital.com)