The word "cyst describes a structure that contains fluid and has skin around it. In the ovary, the majority of cysts during the reproductive years are related to the normal function of the ovary. That is - cysts are a normal housing of eggs while they mature. After ovulation, the cyst that had the egg in it changes to produce hormones and then it resolves. This pattern occurs on a monthly cycle. These cysts are called "FUNCTIONAL Cysts".
Cysts in the ovary that do not go away are not related to the process of ovulation. There are many benign swellings in the ovary - some are tumors, some are small collections of fluid within adhesion's, and so forth. An unchanging cyst over a year is unlikely to be malignant and it is also unlikely to go away.
Free fluid in the pelvis can suggest the rupture of a cyst and leakage of its fluid. This is a transient process and cyst fluid is absorbed within a few days Large amount of fluid can represent an abnormal medical condition such as an infection, liver disease (cirrhosis), heart failure, or a malignancy.