http://www.mayoclinic.com/health/polycystic-ovary-syndrome/DS00423Cyst-- a closed sac, can contain, tissue, air, fluids, or semi-solid material.
Caused by: too much insulin, abnormal development, genetics, inflammation.
Can cause: t2 diabetes, high cholesterol, cardiovascular disease, sleep apnea, endometrial cancer, amongst other things.