Ovulation is the release of a mature egg from an ovary, usually around the middle of the menstrual cycle — though timing varies. A surge in luteinising hormone triggers it, and the egg can be fertilised for about 24 hours, making the days around ovulation the most fertile of the cycle.
Some people notice signs such as clearer, stretchy cervical mucus, a small rise in body temperature, mild one-sided twinges, or light "ovulation spotting." After ovulation, progesterone rises during the luteal phase. Ovulation can become irregular or stop in perimenopause. See the menstrual cycle phases.