Your umbilicus is your bellybutton. It's the place on your stomach where your umbilical cord was attached before you were born. Just call it a bellybutton or navel unless you're a fancy medical writer.
Umbilicus is the official anatomical term for your navel or bellybutton. Most people don't give much thought to their umbilicus, which is really a scar marking the spot where a cord once connected to your source of nutrients when you were a fetus in your mother's body. After babies are born, this cord is cut, and the result is an umbilicus. In Latin, the word means both "navel" and "the center."