The umbilicus, also called the navel, is essentially a scar representing the former attachment of the umbilical cord in the fetus. The colloquial term for navel is belly button. It can form a depression, a type of umbilicus commonly referred to as an innie, or a protrusion, referred to as an outie. The underlying abdominal muscle layer also presents a concavity; its thinness at this point contributes to a relative structural weakness that makes it susceptible to hernia.
One fashion is clothing that leaves part of the lower abdomen with the belly button bare. It is much more common for women than for men. Displaying a bare navel has been a taboo in Western society, as the depression of the navel is taken to be an erotic visual echo. Thus, fashions of display have usually been confined to women and have been perceived as part of liberation and youth movements.