It's a branch of biology that focuses on the development of an organism from a single cell (the zygote) to a complete organism. Embryology covers a wide range of topics, including:

* Gametogenesis: The formation of sperm and egg cells.

* Fertilization: The fusion of sperm and egg to create a zygote.

* Cleavage: The rapid division of the zygote into many cells.

* Gastrulation: The formation of the three germ layers (ectoderm, mesoderm, and endoderm).

* Organogenesis: The development of organs and organ systems.

* Fetal development: The growth and maturation of the fetus until birth.

While embryology primarily focuses on the period before birth, it also provides a foundation for understanding the development of organs and tissues throughout life.