Ovulation; most women are either planning for it, or planning around it. It is the time in a woman's menstrual cycle when she is most likely to get pregnant if she were to have sexual intercourse, and the most likely time she will experience menstrual cramps during her cycle.
During ovulation, there are two basic phases: the follicular phase and luteal phase. These are the basic waxing and waning of ovulation.
The follicular phase begins on the first day of a woman's period. Approximately 14 days (this is an average number for the most average woman and does not indicate the regular cycle of all women) the egg is ready for fertilization. If within 12-24 hours the egg is not fertilized, the egg passes through the woman's Fallopian tubes (the beginning of the luteal phase) and is released into the uterus. The womb sheds it's lining, causing menstruation once again.
If, however, the egg is fertilized, then the body begins producing progesterone, the hormone that supports pregnancy.
Occasionally there are women whose eggs will be released still immature. This condition is called anovulation. A woman experiencing anovulation may miss periods for months or even years, and will often require medication in order to incur pregnancy. When menstruation does occur for these women, very often the period is extremely heavy, and in extreme cases a woman may need to seek medical attention due to blood loss.
If a woman misses her period and home pregnancy tests continue to come up negative, she should seek the consult of a doctor. Usually a doctor will be able to tell from preliminary conversations what the problem is, and prescribe the appropriate medication. If a woman is preventing pregnancy or practicing abstinence, very often birth control pills will be prescribed.
Of course, as always, if you have any questions or concerns regarding your own ovulation, it never hurts to call your doctor.