Define germ layer?

Germ layers are the primary layers of cells that form during embryonic development in animals. There are three germ layers: the ectoderm, mesoderm, and endoderm. These layers give rise to all the tissues and organs of the body. The ectoderm forms the skin and nervous system, the mesoderm forms muscles, bones, and the circulatory system, and the endoderm forms the digestive and respiratory systems.