A woman's reproductive system includes two ovaries. Among other things, the ovaries are in charge of creating two hormones, estrogen and progesterone. These two hormones are necessary to the normal reproductive functions and fertility of a woman's body. However, sometimes the ovaries can develop problems. Those problems can include cysts.
A cyst is a sac that is filled with something, usually some kind of fluid. In the case of an ovarian cyst, the cyst is located on the outside of the ovary.