Final answer:
A cyst is a lesion containing fluid or semi-fluid material, encapsulated in a sac that can develop in various organs including under the skin, the brain, and eyes. They are elevated, firm, and sometimes grow larger, but not all require treatment.
Step-by-step explanation:
A cyst is B. A circumscribed, elevated lesion containing fluid or semi-fluid material. Specifically, a cyst is an encapsulated sac filled with fluid, semi-solid matter, or gas, typically located just below the upper layers of skin. It is notable for being elevated, firm, and sometimes growing over time. Cysts may develop in any organ, with common locations including subcutaneous tissue, the brain, and eyes. These lesions can vary in size and are not always problematic; however, when they become large or painful, medical intervention such as surgery may be necessary. For example, an ovarian cyst is a common, typically harmless condition that affects the ovaries, but can require treatment if it leads to discomfort or complications.