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An ovum (or loosely, egg or egg cell) is a female sex cell or gamete. Both animals and seed plants have ova. The term ovule is used for the ovum of seed plants and for the young ovum of an animal. The word is derived from the Latin word ovum (plural ova) for egg.

In higher animals, ova are produced by organs called ovaries. In the oviparous animals (all birds, most fishes, amphibians and reptiles) the ova develop protective layers and pass through the oviduct to the outside of the body. They are fertilized by male spermacrosome, (2) cell membrane, (3) nucleus, (4) mitochondria, and (5) flagellum (tail) A sperm cell or spermatozoon is the haploid cell that is the male gamete. It is carried in fluid called semen, and is capable of fertilising an egg cell to form a zygote. either inside the female body (as in birds), or outside (as in many fishes). After fertilization, an embryotadpole) of the wrinkled frog Rana rugosa . An embryo is an animal or a plant in its earliest stage of development. Plants In botany, a plant embryo is part of a seed, consisting of precursor tissues for the leaves, stem (see hypocotyl , and root (see rad develops, nourished by nutrients contained in the egg. It then hatches from the egg, outside the mother's body. See egg (biology)In some animals, an egg is the zygote, resulting from fertilization of the ovum. It nourishes and protects the embryo. Oviparous animals are animals that lay eggs, with little or no other development within the mother. This is the reproductive way of many for a discussion of eggs of oviparous animals.

In the viviparous animals (which include humanHuman beings are defined variously in biological, spiritual, and cultural terms, or in combinations thereof. Biologically, they are classified as Homo sapiens ( Latin for knowing man , a primate species of mammal with a highly developed brain. In spirituas and all other placental mammalSubclass Monotremata Monotremata Subclass Marsupialia Didelphimorphia Paucituberculata Microbiotheria Dasyuromorphia Peramelemorphia Notoryctemorphia Diprotodontia Subclass Placentalia Xenarthra Dermoptera Desmostylia Scandentia Primates Rodentia Lagomorps), the ovum is fertilized inside the female body, and the embryo then develops inside the uterusThe uterus or womb is the major female reproductive organ of most mammals, including humans. One end called the cervix, opens into the vagina, and the wider end, called the body of uterus, is connected on both sides with the Fallopian tubes. It comes in a until it is born. It receives nutrition directly from the mother. The ovum is the largest cell in the human body, typically visible to the naked eye without the aid of a microscope or other magnification device.

There is an intermediate form, the ovoviviparous animals: the embryo develops within and is nourished by an egg as in the oviparous case, but then it hatches inside the mother's body shortly before birth, or just after the egg leaves the mother's body. Some fish, reptiles and many invertebrates use this technique.