A human navel.

The umbilicus (also called navel or bellybutton) is a place on the body of mammals that is left after a baby loses its umbilical cord. The umbilicus of humans is in the middle of the abdomen. It is usually only easy to see on humans, and is a thin line on many other mammals. In humans, they can be split into two different kinds, the kind that goes in (innie) and the kind that goes out (outie). Different people have different navels that can be different in size, shape, and looks, but these differences are not genetic (you do not get them from looks passed down in your family). The hepatic portal vein passes from the umbilical vein to the liver. When a person becomes fat, the fat usually goes around the umbilicus.