Polycystic ovary syndrome, or polycystic ovarian syndrome (PCOS), is the most common endocrine disorder in women of reproductive age. The syndrome is named after cysts which form on the ovaries of some people with this condition, though this is not a universal symptom, and not the underlying cause of the disorder. People with PCOS may experience irregular menstrual periods, heavy periods, excess hair, acne, pelvic pain, difficulty getting pregnant, and patches of thick, darker, velvety skin. The primary characteristics of this syndrome include: hyperandrogenism, anovulation, insulin resistance, and neuroendocrine disruption. A review of international evidence found that the prevalence of PCOS could be as high as 26% among some populations, though ranges between 4% and 18% are reported for general populations. The exact cause of PCOS remains uncertain, and treatment involves management of symptoms using medication.

Reference
Wiki: Polycystic ovary syndrome