Egg, or ovum, in biology, female gamete or germ cell, found in all animals and in most plants. Popularly, the term is used to describe those animal eggs that are deposited by the female either before or after fertilization and develop outside the body, such as the eggs of reptiles and birds. The egg is a single cell that develops into the embryo after fertilization by a single sperm cell, or male gamete. In animals, it is formed in a primary sex organ, or gonad, called the ovary. In fishes, reptiles, and birds there is a food store of yolk enclosed within its outer membrane. In plants called angiosperms, the female reproductive organs form part of the flower. The egg cell is found within the ovules, which upon fertilization develop into the embryo and seed.
See also: Reproduction.