It’s short for Polycystic ovary syndrome. It’s an endocrine disorder that in some women causes cysts to form on ovaries, hence the name, but it’s not a universal symptom. It can affect liver function (non-alcoholic fatty liver disease or NAFLD for short), increase cholesterol, cause insulin resistance and type 2 diabetes, sleep apnea, irregular menstrual cycle, pelvic pain (especially if a cyst ruptures, that can cause extreme pain), mood changes, make it difficult to get pregnant.