The process of discharge of ovum from the ovary every month in females is called Ovulation.
When a female child is born, her ovary is already carrying follicles containing primary oocytes which develop in the foetal stage.
These primary oocytes remain as it is till the child reaches her puberty.
At the onset of puberty in female the primary oocytes develop into ova (singular ovum) that start releasing from the ovary during menstrual cycle (a cycle of changes in reproductive system occurring every month).
In each cycle, only one ovum is released which is called ovulation.