An economy consists of the realized economic system of a country or other area, the labor, capital and land resources, and the economic agents that socially participate in the production, exchange, distribution, and consumption of goods and services of that area. A given economy is the end result of a process that involves its technological evolution, history and social organization, as well as its geography, natural resource endowment, and ecology, as main factors. These factors give context, content, and set the conditions and parameters in which an economy functions.

In most birds, reptiles, insects, and fish, an egg (Latin, ovum) is the zygote, resulting from fertilization of the ovum. To enable incubation the egg is usually kept within a favourable temperature range as it nourishes and protects the growing embryo. When the embryo is adequately developed it breaks out of the egg in the process of hatching. Some embryos have a temporary egg tooth with which to crack, pip, or break the eggshell or covering.

Oviparous animals are animals that lay eggs, with little or no other development within the mother. The study or collecting of eggs, particularly bird eggs, is called oology.

Reptile eggs, bird eggs, and monotreme eggs, which are laid out of water, are surrounded by a protective shell, either flexible or inflexible. The special membranes that support these eggs are traits of all amniotes, including mammals.

The 1.5 kg ostrich egg is the largest egg currently known. The Bee Hummingbird produces the smallest known bird egg, which weighs half of a gram.