Germ layers are the three primary layers of cells formed during the early development of an embryo. These layers are called the ectoderm, mesoderm, and endoderm. Each layer gives rise to different tissues and organs in the body. For example, the ectoderm develops into the skin and nervous system, while the mesoderm forms muscles, bones, and the circulatory system. The process of germ layer formation is known as gastrulation. During this stage, cells migrate and differentiate to establish the three layers. Understanding germ layers is crucial in fields like embryology and developmental biology, as they provide insight into how complex organisms develop from a single fertilized egg.