Oogenesis is the production of ova (egg cells) in females by meiosis.
A primary oocyte undergoes meiosis I to produce one haploid secondary oocyte, and one polar body. The secondary oocyte will be released from the ovary and has the potential to be fertilized by a sperm cell.
The secondary oocyte undergoes meiosis II if it becomes fertilized. At this point the egg cell is referred to as an ovum. Once the sperm enters the ovum, and nuclear fusion of the two cells occurs, a new diploid cell is created, called a zygote.