Fertilisation (also known as conception, fecundation and syngamy) is the fusion of gametes to produce a new organism. In animals, the process involves the fusion of an ovum with a sperm, which eventually leads to the development of an embryo. Depending on the animal species, the process can occur within the body of the female in internal fertilisation, or outside (external fertilisation). The entire process of development of new individuals is called reproduction.