In fish, the term egg usually refers to female haploid gametes. In reptiles, birds, amphibians and insects the term egg refers to a fertilized ovum with protective and nutritive tissues.

• 卵以鱼类而言，卵通常是指为雌性所产之配子。而在爬虫类，鸟，两栖动物与昆虫，卵是指受精之后的合子。