The exoderm is an outer embryonic layer of cells that develops in some animals. Synonyms for exoderm include ectoderm, epidermis, outer layer, and surface tissue. The ectoderm refers to the outermost layer of cells in animals, which gives rise to the nervous system, skin, and other structures. Epidermis specifically refers to the outermost layer of cells in the skin, which provides a protective barrier for the body against external harm. The outer layer can also be used to describe the top layer of cells in any organ or tissue. Surface tissue is another term that can be used to describe the outermost layer of cells on various structures.