A synovial cyst is a fluid-filled sac that forms near a joint or tendon, often in areas like the knee or wrist. These cysts develop from the synovial membrane, which produces synovial fluid to lubricate joints. When the membrane becomes damaged or inflamed, excess fluid can accumulate, leading to the formation of a cyst. Synovial cysts are usually benign and may not cause symptoms. However, if they press on nearby nerves or structures, they can lead to pain or discomfort. Treatment options include observation, aspiration (draining the fluid), or surgical removal if necessary.