Embryonic development is the process by which a fertilized egg, or zygote, transforms into a complex organism. This journey begins with cell division, where the single cell divides multiple times to form a cluster of cells called a blastocyst. As development continues, these cells start to specialize, forming different tissues and organs. During this time, the embryo undergoes several stages, including the formation of the germ layers, which eventually give rise to all body structures. By the end of the embryonic period, the basic body plan is established, setting the stage for further growth and development into a fully formed fetus.