Here's a breakdown of the stages:

* Zygote: The first cell formed when a sperm fertilizes an egg.

* Embryo: The developing organism from about two weeks after fertilization until the end of the eighth week of pregnancy. During this time, all major organs and body systems start to form.

* Fetus: From the ninth week of pregnancy until birth. The fetus continues to grow and develop, with organs maturing and becoming functional.

So, the embryo is the early stage of development, and it transitions into a fetus as development progresses.