Since the domestication of poultry birds, a lot of information has been provided on production system, reproductive potentials, genetic improvement and feeding strategies. Unfortunately, little is known about the unique nature of the blastodisc in the yolk of poultry birds' egg. Consequently, information on poultry birds egg characteristics, formation, quality as well as the biological, nutritional and cultural values of poultry birds egg were provided. Ovulation of large mass of yolk containing the blastodisc from the left ovary only and the subsequent formation of shelled egg within the body cavity is peculiar to avian species. However, there are some similarities between the blastodisc in the poultry birds and the ovum in other animal species. The yolk has vitelline membrane that serves as barrier to the blastodisc that obtains nourishments from the yolk for growth and development. It is ovulated into the oviduct, where it is fertilized if mated exactly as found in other animal species. Therefore, blastodisc could be described as the actual egg cell and the only living portion of the poultry birds' egg which develops into embryo. If the shelled egg is fertilized and incubated, it becomes a hatchling and if consumed like the unfertilized egg it sustains life. Consequently, poultry birds' egg could best be defined as an egg inside egg that gives and sustains life".