The navel (also known, colloquially, as the belly button or, clinically, as the umbilicus) is a scar on the abdomen, caused when the umbilical cord is removed from a newborn baby. All placental mammals have a navel. It is fairly conspicuous in humans.
In humans, the scar can appear as a depression (often referred to colloquially as an innie) or as a protrusion (outie). Although they can be separated into these two categories, navels actually vary quite widely among people in terms of size, shape, depth/length, and overall appearance. As navels are essentially scars, and not in any way defined by genetics, they can serve as a way of distinguishing between identical twins in the absence of other identifiable marks.
The umbilicus is an important landmark on the abdomen since its position is relatively consistent among humans. The skin around the waist at the level of the umbilicus is supported by the tenth thoracic spinal nerve (T10 dermatome). The umbilicus itself lies at the level between L3/L4 vertebrae.