Final answer:
From the second to the eighth week of gestation, the developing organism is known as an embryo.
Step-by-step explanation:
The organism that develops from the second to the eighth week of gestation is called an embryo. During this vital period of development, the embryo undergoes significant changes, with cells dividing, migrating, and differentiating to form the rudimentary structures of all organ systems. Although these systems are not fully functional at this stage, by the end of the embryonic stage, the groundwork for further development into a fetus has been established, paving the way for the next phase of prenatal development.