What is "germ layer"

n. (context embryology English) A collection of cells assembled during embryogenesis that eventually develop into all tissues and organs via organogenesis in animals.

n. (embryology) any of the 3 layers of cells differentiated in embryos following gastrulation

A germ layer is a primary layer of cells that form during embryogenesis. The three germ layers in vertebrates are particularly pronounced; however, all eumetazoans, ( animals more complex than the sponge) produce two or three primary germ layers. Animals with radial symmetry, like cnidarians, produce two germ layers (the ectoderm and endoderm) making them diploblastic. Animals with bilateral symmetry produce a third layer (the mesoderm), between these two layers. making them triploblastic. Germ layers eventually give rise to all of an animal’s tissues and organs through the process of organogenesis.