What is the term "zygote" defined as?

The term "zygote" specifically refers to the single cell that is formed when an egg and sperm unite during the process of fertilization. This single cell contains a complete set of DNA from both parents and is the very first stage of a developing embryo. The zygote undergoes rapid cell division and eventually forms a blastocyst, which will implant in the uterine wall to begin the next stages of development.

While the beginning of fetal development and various stages of embryonic growth are important concepts in understanding the overall process of reproduction and development, they refer to phases that occur after the zygote stage. The term does not specifically denote a fertilized egg before implantation, as that stage is often referred to as a pre-implantation embryo. Hence, the definition of "zygote" is accurately captured by the description of the cell formed at the moment of fertilization.