The belly button, or navel, is a small indentation on the abdomen that marks the spot where the umbilical cord was attached during fetal development. This cord connected the developing baby to the placenta, allowing for the exchange of nutrients and waste. After birth, the cord is cut, and the remaining stump eventually falls off, leaving the belly button. Belly buttons can vary in shape and size, and they are classified as either innies or outies. An innie is a recessed belly button, while an outie protrudes outward. The belly button has no significant biological function in adults but can be a site for piercings or a point of interest in body art.