Final answer:
The developing baby is known as an embryo during the first two months post-fertilization; after the embryonic period, it is termed a fetus.
Step-by-step explanation:
During the first two months of pregnancy, the developing baby is called an embryo. This term describes the early stages of fetal development, from conception to the end of the 8th week. At the end of the embryonic period, all of the organ systems are present in a rudimentary form.
After the 8th week, the developing baby enters the fetal stage, which lasts until birth. It is during this period that the fetus grows in size, and organs continue to mature and develop.