Ovum

The ovum (plural ova) was the female reproductive cell in certain species, including Humans. After external fertilization by a male's sperm, an ovum would give rise to an offspring. Sometimes, the mating process could produce several offsprings at a time. In cases where a single fertilized ovum split, several genetically identical children were produced. When separate ova were fertilized at the same time, it gave rise to ordinary siblings who happened to be born at the same time, but were genetically dissimilar.