Ovarian cysts are fluid-filled sacs on the ovaries that are often asymptomatic but can cause abdominal or pelvic pain. They can be categorized into functional cysts, benign neoplastic cysts, endometriotic cysts, and malignant cysts, with functional cysts being the most common type. Diagnosis typically involves imaging tests, and while many cysts resolve without treatment, some may require hormonal therapy or surgery.