Cysts are closed sacs filled with fluid, air, or other substances that can form in various parts of the body. They can vary in size and may develop in organs, tissues, or under the skin. Most cysts are benign, meaning they are not cancerous, and many do not cause symptoms or require treatment. However, some cysts can become painful or lead to complications if they grow large or become infected. Common types of cysts include sebaceous cysts, ovarian cysts, and baker's cysts. Diagnosis often involves imaging tests, and treatment may include drainage or surgical removal if necessary.