The new cell formed by the union of an egg and sperm.
When an egg becomes fertilized by the sperm, the resulting one-celled entity, called a zygote, immediately begins to develop. The zygote starts out as a microscopic speck. Three days after fertilization, though, the zygote increases to around 32 cells, and within a week it has grown to 100-150 cells. These first two weeks are known as the germinal period.
In humans and higher animals, the cell formed by the union of the sperm cell and the egg cell of the parents and from which a new individual will emerge is called zygote.