An embryo about 6 weeks after fertilization at the left, together with a fetus at about 10 weeks development at right, courtesy Ferrylodge, via Wikipedia
In humans, an embryo is the first stage of development of a fertilized egg during pregnancy. At this stage, it implants itself into the uterus, which is lined with epithelial cells that begin to provide it with nourishment and eventually develop into the placenta. After 8-10 weeks, it is then referred to as a fetus.