What is an embryo?

An embryo refers to an organism in the earliest stage of development, typically following fertilization and prior to developing into a fetus. This stage is crucial as it encompasses the initial formation of major organs and structures. The embryonic phase begins immediately after an egg is fertilized by a sperm, leading to a series of cell divisions and the eventual formation of tissues and organs. This understanding is fundamental in biology and medicine, particularly in fields such as developmental biology and obstetrics.

The other options describe different phases or concepts in the life cycle of organisms. A fully developed organism would indicate maturity, while a stage of fetal development refers to the later period after the embryonic stage, when significant growth occurs. A type of cell division typically pertains to processes like mitosis or meiosis, which are fundamental biological processes but do not define what an embryo is. Therefore, recognizing the embryo as the earliest stage of development encapsulates its critical role in the progression of life.