Ahernia in the umbilical area occurs when a structure protrudes through the abdominal wall. this is an example of a/an:

This is an example of a myocele.
A myocele is a medical term describing the protrusion of muscle tissue through a tear in the fascia surrounding it. A fascia is a unit of connective tissue (most probable collagen) which is beneath the skin and it encloses, stabilizes and separates muscle and internal organs. Myoceles (or muscle hernia) mostly occur in the lower part of the body and mainly below knee level.