What is the name of the cell formed immediately after fertilisation?

The cell formed immediately after fertilization is called a zygote. This single cell represents the earliest stage of development in a new organism, resulting from the fusion of a sperm cell and an egg cell. The zygote contains a complete set of genetic material; it is diploid, meaning it has a full set of chromosomes with genetic contributions from both parents.

After conception, the zygote undergoes several rounds of cell division, eventually forming a multicellular structure that will develop into an embryo. The term "embryo" refers to a later stage in development after the zygote has started to divide and grow. The term "fetus" is used to describe a developmental stage that occurs much later, after the embryo has developed into a recognizable form of the organism. "Gamete," on the other hand, refers to the reproductive cells (sperm and egg) that combine during fertilization to create the zygote. Thus, zygote is the appropriate term for the cell immediately following fertilization.