What is the term for a fertilized egg?

The term for a fertilized egg is "zygote." When the sperm fertilizes the ovum (egg), it forms a single cell known as the zygote. This is the initial stage of development that marks the transition from a gamete to a new organism. The zygote undergoes several divisions and developments, eventually transitioning into an embryo, which is the term used for this developing organism in the following stages.

The other terms refer to different stages or types of cells involved in reproduction and development. An ovum refers specifically to the female gamete or egg before fertilization, while a blastocyst is a later stage of embryonic development that occurs after the zygote has divided and formed a hollow structure that will implant in the uterus.