Eggs come from a wide array of oviparous species, such as birds, fish, reptiles such as snakes, tortoises and frogs, and many insects. The most common egg comes from chickens. There are more species that lay eggs than there are species that have live births.
Eggs form inside the oviparous species in the reproductive process. In the case of chickens, eggs form over a period of around 25 hours. Some animals' eggs are fertilized internally, and some animals' eggs are fertilized after they have been laid.
Commercial chicken eggs are not fertilized. Chicken eggs that are fertilized eventually hatch into chicks if the reproductive process is successful.