What is the medical term meaning Swelling behind knee caused by synovial fluid?

The medical term for swelling behind the knee caused by synovial fluid is popliteal cyst. It is also known as a Baker's cyst, after the British surgeon who first described it in the 18th century. Popliteal cysts are fluid-filled sacs that develop behind the knee joint. They are caused by an accumulation of synovial fluid, which is the lubricating fluid that helps to keep the knee joint moving smoothly. Popliteal cysts can range in size from small and painless to large and painful. They can also cause problems with knee movement and stability. Treatment for popliteal cysts may include rest, ice, compression, and elevation. In some cases, surgery may be necessary to remove the cyst.