When a ready-to-be -fertilized egg drops out of your ovary. About two weeks after menstration.
You don't ovulate when you are pregnant.
Only in Dogs. In humans and other species multiple births are cause during the ovaluation period.
It seems there may have been a typo. If you meant ovulation, it is the process in which a mature egg is released from the ovary, ready to be fertilized by sperm. This usually occurs around the middle of a woman's menstrual cycle.