In human females, ovulation is the phase in the reproductive cycle where an egg is released from an ovary to travel through the fallopian tube towards the uterus. It occurs one approximately every 28 days. Puberty in women is marked as the start of ovulation (generally at around the age of 13, but this can vary somewhat), and the end of ovulation marks menopause.
At ovulation, the uterus is changed by hormones to become more hospitable to the egg should it become fertilized. If the fertilized egg implants in the uterus, the uterus forms a placenta. However, if this does not occur, the lining is shed in menstruation.