Ovum: An egg in the ovary of the female. This egg is called the female gamete or sex cell. It combines with the male gamete, called a sperm, to form a zygote. This formation … process is called fertilization.. One type of miscarriage occurs when the egg does not develop into an embryo following th…. 2  The Ovum: Its Definition and Role in Infertility The basic definition of ovum is a common topic in elementary school biology. 3  Learning about the definition of the oveum and its role in fertility is not hard.