Embryonic development refers to the process by which a fertilized egg develops into an embryo and eventually into a fetus. This stage in the life cycle of an organism is characterized by rapid cell division, growth, and differentiation as the embryo forms various organs and systems necessary for survival outside the womb. Embryonic development occurs during the first few weeks after fertilization and typically takes place within the female reproductive system until it reaches a stage known as a blastocyst, at which point it may be implanted into the uterus or used in assisted reproduction techniques such as in vitro fertilization.