Anovulation means lack of ovulation, or absent ovulation. Ovulation, which is the release of an egg from the ovary, must happen in order to achieve pregnancy. If ovulation is irregular, but not completely absent, this is called oligovulation. Both anovulation and oligovulation are kinds of ovulatory dysfunction. Ovulatory dysfunction is a common cause of female infertility, occurring in up to 40% of infertile women.
Usually, women with anovulation will have irregular periods. Or, in the worst case, they may not get their cycles at all. If your cycles are shorter than 21 days, or longer than 36 days, you may have ovulatory dysfunction.
Also, if your cycles fall within the normal range of 21 to 36 days, but the length of your cycles varies widely from month to month, that may also be a sign of ovulatory dysfunction. (For example, one month your period is 22 days, the next it's 35.)